Imagine you're the product manager for Facebook Marketplace. Since many sellers don't mark items as sold, what existing functionality and metrics could you use to determine whether an item has likely sold?

Question

Imagine you're the product manager for Facebook Marketplace. Since many sellers don't mark items as sold, what existing functionality and metrics could you use to determine whether an item has likely sold?

Asked at Meta (Facebook) over a year ago

20.9k views

Asked at

20.9k views

How to answer Technical questions

Interview Guide

Liked by PM Exercises

Paul Booth

Silver PM

May 24, 2020

This was a really fun Facebook technical question to answer. Its very easy to make things more complicated :P

I will focus on three specific areas to answer this question:

Framing:
- What problem are we solving and how it relates to the company mission
- Users
Goals:
- Goals of this (data) product
- Establish a criteria for success
Solutions:
- Review of existing product functionality
- Propsed Metrics

Initial Problem

Many sellers don't mark items as sold on FB Marketplace, what existing functionality and metrics could be used to determine whether an item has likely sold?

I would first confirm that - based on the phrasing - the interviewer wasn't restricting the answer to use existing metrics. I will assume for this the answer is no - existing functionality, and any metrics I can come up with based on those functionalities and known data.

Linking to the Company mission

The company mission is worth keeping in mind here: enable people to build communities and bring people together. While a marketplace is not expected to trigger new friendships, a busines and less formalised trading between people are a postive reflection of a community with trust and safety. Whether physical or online/virtual, it is vital there is trust between buyers and sellers and also in the quality of the product being traded. The transaction must also be trusted as safe, or with a mechanism to reclaim ones money back in the event of fraud.

Much of that trust is dervied from the platform, who is expected to provide tools and services in the form of buyer/seller ratings, supporting issues with bad actors etc. In the real world, when we shop in a market we assume a local council or market organiser have vetted the stall owner in some way - in other words, our perception of a maket and its sellers are interconnected. If we have a bad experience with one seller, we may lose trust that other bad actors are not being weeded out.

People are able to share posts about a new marketplace item into FB Groups, these communities need to trust what they see are as described. Relating this to the problem at hand - people need to trust that the items they see are available and not already sold.

We will take the overall mission of the FB Marketplace team as: enabling people and businesses to safely and efficiently buy and sell goods to other FB users. FB Marketplace does not facilitate delivery or the exchange of money.

Users

The user we are focusing on is the seller since the question states that many sellers don't mark items as sold. In other words, it' not every seller. Sellers have to manually mark an item as sold, so why might some users not do it?

- The seller is not aware of the feature to mark items as sold

- The seller forgot or is not in the habit of doing it

- The seller sees no advantage (or no motivation to avoid a potential disadvantage) by not doing it

- The seller is deliberately not doing it

Some of these overlap with possible user categorisation relating to the level/type of marketplace experience a user has:

- new/first time seller

- infrequent seller

- frequent seller

- formalised business (which can then also be either a new, infrequent, or frequent seller)

- a criminal or fraudster

Plus of course, sellers are rated on the marketplace! However, ratings are not specific to an item, just to the seller

Additionally, Facebook has data on the friend community of each seller on Facebook itself including Messenger, and potentially on Instagram and Whatsapp also. The account itself may hold clues in terms of online behaviour with the platform(s) and with friends.

To summarise, the existing functionalities relating to users we can utilise and analyse data about are:

1. Seller ratings / feedback / reports from other users

2. Seller behaviour on FB marketplace

3. Seller experience and business status on FB marketplace

4. Seller's personal FB / Insta / Whatsapp networks and behaviour

Goal

Our goal is to reliably identify items which are likely to have been sold but have not actually been marked as sold by the seller

Success:

a high degree of accuracy when identifying items are being likely sold, but not marked as sold by the seller

Existing functionalities:

1. Buyers rating sellers: After trading with a seller, a buyer will rate them. True and fair buyers would not rate a seller if they have not purchased from them. So, assuming we have high confidence that a buyer has actually purchased an item we can utilise this in our metrics.

2. Marketplace seller ratings: Based on when a seller recieves a rating

3. Behavioural data: Segmentation of sellers based on their behaviour, status and potentially their personal network.

4. Messages: NLP analysis of buyers' messages to sellers asking if items are still available, which have gone unanswered

5. Data analysis and machine learning are applied to create a confidence score for all items not marked as sold. Utilising the experitse of data science we could apply ML techniques to analyse items. However, depending on the ML technique(s) applied it may require good training data. FB has scale, but the training data would need to include items that are known to be sold and known to be unsold. Given that we are trying to identify the latter, some ML techniques may not be appicable. I would work with data science to see what is possible.

6. People reporting items to Facebook directly as listed incorrectly: This is the easiest and most convenient, but works on the assumption that people will report items as not properly marked. There is no mechanism for buyers to confirm they have recieved the item (which there is on eBay for example), which would also help to infer an item was sold.

Metrics:

Based on the above, possible metrics could be:

- confidence score for sold items: could be derived by data science team or by a formula using multiple metrics below.. assuming there is a confidence score we could simply have:

- count of items likely sold (filtered by those where confidence score is high; assuming a simple categorisation of Low, Med, High)

Metrics (assuming the above confidence score is NOT available):

The metric names will likely be verbose to make them clear, I would find shorter and simpler names with more time...

- Inferred purchase: Using data that a buyer has rated a seller to infer an item was purchased. The difficulty here is identifying which item a person has actually purchased as the transaction and shipping are not facilitated by FB. However, we can utilise data about items a person viewed, liked, saved, commented on or asked the seller a question about to infer which item it was.

- Unanswered item status requests: the number of times buyers ask if items are still available which were not answered or not answered in the affirmative.

- Item time on marketplace or "time since posted": how long an item has been on the market (this assumes older items are more likely to be sold, which may not be true for some items which are not at all popular and where the seller wants to hold out for a sale)

- Sellers not likely to mark items as sold: (based on the behavioural analysis mentioned earlier). This assumes a confidence interval can be created from the analysis of behavioural data - this would enable a 'grade' or index to be created. Based on the grading, this metric only counts the sellers above a certain threshold.

- Fraud flag: true/false to indicate that a flag marker is placed on the account due to bad ratings, comments, or reports from other marketplace users.

Using this data, I can see the potential to create a mechanism to send notifications to sellers to simply ask them if an item has sold. Ideally, that seller could answer Y/N directly in the FB notification to reduce friction and remove the need for an extended user journey. If users have multiple suspected unsold items, then targetted training messages could help e.g. an email that explains the situation with their items and shows them how to mark them all as sold.

16 likes | 1 feedback

1 Feedback

Bijan

Platinum PM

May 25, 2020

Interesting solution. And as you mentioned, this is a tricky one. There are really 3 questions here:

a problem solving one : what is the cause of the problem?
a product design one : how would you solve it?
a metrics one : what metric would you use to measure the succss of your new proposed feature?

I think the right approach is to solve for each of the above in the order listed. And that's what you did. Here is my feedback:

Things done well:

You listed potential causes of the problem
You focused on solving for those problems using existing functionalities as the question asked
You listed great set of meaningful metrics to help you measure the success of ability to detect the posts for sold items

Areas of Improvement:

Consider evaluating and prioritizing the metrics - mention your primary and secondary metrics

Good answer overall. Looking forward to seeing more from you!

4

Top Meta (Facebook) interview questions

What is your favorite product? Why?89 answers | 263k views
How would you design a bicycle renting app for tourists?62 answers | 82.5k views
Build a product to buy and sell antiques.54 answers | 66.8k views
See Meta (Facebook) PM Interview Questions

Top Technical interview questions

What happens when you enter a URL in your browser?6 answers | 10.8k views
How does TinyURL work?5 answers | 317k views
How would you determine how to rank posts in the newsfeed?4 answers | 3.3k views
See Technical PM Interview Questions

Invite members
Invite by email

Add another

KONDAMURI DHARMA SASTHA SAI SRI HANUMA · Answer 1 · 2024-10-17T08:28:57+0000

My Approach:

First, I would analyze Facebook Marketplace, focusing specifically on understanding when an item is sold. This insight is critical to identifying user behaviors that frequently occur after a sale, enabling us to track relevant metrics.

Objective: Improve the buyer experience on Facebook Marketplace.

Overview of Facebook Marketplace

Definition & Functionality:

Facebook Marketplace allows users to buy and sell items by posting listings on the platform. Users can negotiate and gather additional information through chat, with no fees for either buying or selling. Listings can be promoted on a user’s wall or within relevant groups, and all communication related to the sale happens within the listing’s chat.

User Journey: Seller's Perspective

Since the focus is on sellers, we’ll observe their journey and correlate actions with potential metrics to track.

-Identifies an item to sell.

-Lists the item on multiple marketplaces, including Facebook.

-Waits and promotes the listing on Facebook.

-Engages with potential buyers as they reach out.

-Replies to comments on shared posts.

-Responds to queries and builds conversations.

-Engages in conversations with multiple buyers simultaneously.

-Finalizes a buyer, then:

-Connects with them.

-Sells the item.

-Notifies other interested buyers that the item is sold.

Behavior After Sale:

After completing a sale, sellers often exhibit specific behaviors, this is mainly due to a few reasons, they might not be aware of the delisting feature Facebook can check with the users from time to time. They don't feel incentivized by the behavior, they do not see a point in doing it

-Conversation Drop-off: Simultaneous decline in multiple active conversations.

-Post Engagement Cessation: Discontinued activity on shared posts.

-Message Reduction: Decline in responses to messages or a shift to one-word replies.

-Marketplace Activity Decline: Reduced logins or engagement on Facebook/Marketplace.

These behaviors result in observable drops in several key metrics:

Active Conversations: Sudden reduction in ongoing chats.

Reply Rate: Decreased rate of responses to comments.

Message Volume: Decline in average messages per conversation.

Session Count: Fewer logins or sessions on the platform.

Metrics to Track:

Drop in active conversations post-sale.

Decrease in replies to comments on Facebook posts.

Reduction in average messages per conversation.

Lowered reply rate across interactions.

Decrease in logins or sessions, indicating reduced Marketplace activity.

Conclusion

By leveraging these behaviors and metrics, Facebook Marketplace can proactively infer when an item is likely sold, keeping listings relevant and buyer experience optimal. Testing these indicators can refine their accuracy, improving the platform’s usability.

Rafa · Answer 2 · 2022-01-23T07:46:07+0000

The Marketplace Product: the Marketplace allows people to trade with other people, usually around used stuff.

The problem: Presenting items that are not relevant in the marketplace hurts people that are looking for such items. The response rate might be low, people might be disappointed about a negative response, and it hurts the trust in the Marketplace.

The buyer user journey:

Find something that you are interested in.
Watch images\videos and read about the item.
(optional) talk to the person and get additional information. The communication can be done via FB messenger or some other communication channels.
(optional) schedule a meeting to see the item.
Payment
(optional) Delivery

The seller user journey:

Set the product you’re willing to sell (details, classification, images, location, etc. )
(optional) Set additional channels for communication.
(optional) talk to the person and get additional information. The communication can be done via FB messenger or some other communication channel.
(optional) schedule a meeting to present the item.
Receive the payment.
Hand over the product / (optional) Delivery.
Mark the item as sold.

Why don’t sellers mark the item as sold?

They are not aware that it is an option.
They don’t understand the benefit of it (they were exposed to the messaging but decided to ignore it)
They are not here
- They might use the Marketplace only for selling a single item.
- They might use Facebook only for selling a single item.
- They might use their email address only for selling the item.
Intentionally, they want to hurt buyers\Marketplace\Facebook.

I can think of three approaches to reduce uncertainty around sold\unsold items:

Asking
Assuming
Knowing

Asking

Mostly, the person who knows whether the item is still relevant is the seller.

The most accurate response will be from the seller.

We can have a few processes to verify it with the seller:

Reactivation of the listing - every item will be posted on the marketplace for two weeks. If the seller interested in continuing the listing, they need to confirm that it is still relevant. Each reactivation will get the item additional two weeks.
Periodical reminders - asking the seller whether the item is still available - the notifications can be push notifications, web, mobile, and email. The reminders can occur once a week.
Post communication confirmation - a day after we identify communication between the seller and a potential buyer\s (a buyer is someone who reviewed the item) that occurs on FB or WhatsApp, we will send a message to check if the item is still relevant.

Assuming

Sometimes we don’t know since we haven’t received a response from the buyer.

There are a few metrics that can assist us in scoring the item, and if it goes above some threshold, we can mark it as potentially sold and deprioritize it in the view.

The seller’s FB’s visits frequency dropped.
The seller’s messages response rate dropped, there was an increase in response time, or messages were kept unread.
Read (ML) of FB\WhatsApp messages (“not relevant”, “sold”, “sorry”, “apologize”).
Proximity of potential buyers to the seller (location-based FB’s app ).
Ask suspected buyers whether they bought the item.
Seller’s FB activity - post \ story about the item.

Knowing

Manage the transaction via FB - if a transaction is made using FB’s payment service.
Deliver the product - if FB extends and does the delivery or works with 3rd parties.

I will not continue here to prioritization and suggestions.

Will love to hear your thoughts and feedback

neeraj gather · Answer 3 · 2020-05-21T08:43:55+0000

Product Description - Facebook Marketplace is an interface for people to buy and sell things locally or shipped, though FB doesn't go into the transactions & logistics of the trade.

Goal - To identify if an item has likely been sold

Users - Buyers and Sellers (For our goal lets focus on seller)
User Journey (Seller):
1. Seller lists an item/stock to be sold on FB Marketplace and add the description, photos and other details
2. Seller gets option to boost, edit, remove the listing.
3. Seller gets added to a group conversation with buyer if some buyer is interested in enquiring more about the product
4. Seller can clarify the details with buyer and both the parties can collaborate to complete the trade (Delivery, Payment etc.)
5. Seller also gets an option to mark item as sold
6. Seller also gets an option to mark item as pending - possibly meaning that item is out of stock

Problem - Sellers usually don't mark the item as sold even if it has been sold. And since the trade is happening between two parties personally with no involvement of FB, it is struggling with identifying which items have been sold.

Possible functionality based solutions -
1. If there is any boost/renew request raised by seller in last week/month. If seller is requesting for a boost/renew, it is likely that item is not sold yet.
2. If there is any recent update made the seller in the listing. If seller has edited some detail in the listing, it is likely that seller is still trying to sell the item.
3. If seller has recently listed the item on other forums (For ex. buy and sell). Again, it tells seller is trying to sell the item.
4. If seller is joining the buyers' enquiry groups. i.e. if a buyer makes a messanger enquiry about the item, FB creates a group between this buyer and the seller to initiate the conversation. Seller gets an option to join this group to take the conversation forward. so if a seller is not joining these groups, it is likely that item has already been sold.
5. If a buyer reports the item as sold. i.e. if buyer finds out from seller in the conversation that item has been sold and goes on to raise a report against the same as it should have been marked as sold by the seller to respect buyers' time.

Possible metrics based solutions -
1. The length/duration of the chat on this listing. If the length of chat is less or if seller responses are not more than two sentences, FB can assume that seller is not interested in selling this item to the buyer and its possible that item has been sold. But we need to analyse if FB can do that without compromising on chat privacy. And FB can send out a notification to seller to confirm if the item has been sold or not.

Other possible solutions -
1. FB starts charging once the duration for which a listing can be kept freely is passed, let's say 3 months. This will encourage sellers to remove the items that are either sold or are not showing any response. But we do need to look into the side effects this strategy could have on the bigger goal of the Facebook which will depend on the stage of product life cycle.

Thanks. Please share your feedback.

Nishant Kumar · Answer 4 · 2023-12-17T07:46:35+0000

CQ:

What is FB Marketplace - match sellers & buyers for goods being sold in the locality; only for listing, financial txn is not supported
App or web - app
Geography - Not relevant
Goal - Drive engagement

User Journey:

Sellers listed the product
Post appears on marketplace/timeline
Post gets reaction - comment/likes
Seller & buyer either interact on FB or offline to complete the txn
Seller marks the product as sold or leaves the product as it is

The use case here is similar as of Matrimonial, property rent/buy where after the user’s goal is met they don’t necessarily update the status on the market place.

What would happen is that user would first create & publish a post, interact with people (on the post, on the native msg box, or initiate offline communication), when the deal finally gets done then they would stop interacting on the portal.

Metrics:

After the post went live,
1. % users who stopped interacting on the post within 7 days (figure would depend on avg deal closure time, depends on nature of product, geography, demographics etc.)
2. % users for whom sudden drop in daily activity by x% is observed within the post reactivation window (assume its active for 2 weeks)
  1. Supporting trigger -
    1. % instances wherein we see contact exchange b/w seller & buyer
    2. Offline interaction (outside FB)

Noah Weingart · Answer 5 · 2022-08-31T18:13:54+0000

Imagine you're the product manager for Facebook Marketplace. Since many sellers don't mark items as sold, what existing functionality and metrics could you use to determine whether an item has likely sold?

Understand the question
1. Ask questions to narrow the scope

To make sure – Facebook Marketplace is generally B2C? Not a lot of commercial listings?

Yes

Does a user need to have a Facebook account to list on Facebook marketplace?

Yes

Does Facebook have a way to process payments within marketplace?

No

Describe the product
User Journey - listing a product as a seller
1. User logs into Facebook using credentials
2. Navigate to Facebook marketplace
3. Click “Add Item”
4. Enter title and description
5. Upload photos
6. User has the option for paid promotion
7. Select a price or negotiable (is this a thing?)
8. Wait. User may check periodically to view pageviews etc
9. User receives messages through facebook messenger
10. Once a price agreement is reached and logistics worked out, furniture is delivered
11. Payment is generally done offline
12. To de-list a product, the user needs to log into FB marketplace and removes the listing
13. Review the buyer
User Journey - buying a product
1. User logs into Facebook
2. Navigate to marketplace
3. Search or browse for product of interest
4. Find the product of interest
5. Message seller
6. Work out logistics and payment amount
7. Transact. Pay using cash, venmo, zelle, etc.
8. Bring item home
9. Maybe there’s a way to indicate that the user bought the item?
10. Review the seller/product
1. Select attributes (this is really potential metrics)
- Time between initial posting and sale of the item
- Percentage of items removed or marked as sold (not “zombie”)
- Percentage of items with paid promotion
- Number of transactions completed through FB marketplace
- Number of items posted on FB marketplace
- % of reachouts that receive a response from the seller after the initial reachout
- Number of weekly check-ins on views etc from seller
- % of buyers that get reviewed
- % of sellers that get reviewed
1. Select a goal
- Decrease the % of zombie items – items defined by lack of activity for a specified period of time (no views, sales, etc.)
  - Zombie items can also be defined as those for which sellers do not respond
As a shopper, I want to contact sellers about items that are currently available so that I can optimize my shopping experience
1. Prioritize attributes
1. % of buyser and sellers that get reviewed
2. % of initial reachouts that receive a response
3. % of items removed or marked as sold after 1 month
4. Number of weekly check ins by the seller
5. Time between initial posting and sale/removal of the item
1. Design the product
Ideas:
- Mark item as unavailable if a threshold is reached where the seller isn’t responding to new inquiries about the item
  - You’re never really going to know if the item is sold, taking it off the marketplace might be the closet thing
- Mark item as unavailable if the seller hasn’t checked on it over a certain period
- You could also use NLP within facebook messenger to determine if an item has sold
  - Things like “thank you, great purchase!”
- Reviews of sellers and buyers
  - This is a proxy for saying a transaction has finished – you get definitive knowledge that the item has sold
  - This probably already exists
- Start taking payments within facebook marketplace
  - This is outside of the confines of the prompt as it doesn’t use existing functionality
1. Think about trade-offs
Top contenders:
1. Encourage more reviews through emails when a seller or buyer hasn’t checked on an item in a while
  1. Pro: very sure way of knowing if an item has actually been sold
  2. Probably is already done
  3. Not sure if there is room for improvement here
2. NLP to decipher when an item has likely sold. Can send a confirmation email to buyer and seller to allow them to veto. Combine this with inactivity metrics to make the guesses better.
  1. Technically more difficult
  2. High penalty if you get this wrong
  3. Requires no additional interaction from the user
  4. LIkely to miss offline comms (done via text or phone call)
1. Summarize the answer
Going to go with natural language processing, as it is very easy from the consumer side and reasonable to implement in terms of effort. My guess is that you could detect a higher number of cases where an item is sold, although it probably won’t completely fill the gap.

Palash Kala · Answer 6 · 2020-08-31T18:21:22+0000

I am not really aware of Facebook Marketplace
Can I ask a few clarification questions?
- Can you explain in brief what is facebook marketplace?
- Who are the buyers and sellers and what kind of things are sold on facebook marketplace
- Can you explain the process of how seller adds a new item
- And what happens when a buyer buys it
I will answer this question as follows
- First, I will describe the typical seller and buyer journey
- Cases when we can say that the product has been sold
- Identify the best case
- What technology will be able to help
- Identify the best solution
User journey
- Discover
  - Go through categories
  - Search for a product
- Buy
  - Either
    - Make offer or
    - Message seller
  - Negotiate
  - See the product
  - Confirm
  - Make payment
- Sell
  - Go through categories
  - Add a product
  - Either
    - Receive a notification for an offer
    - Message from prospective buyer
  - Negotiate
  - Show the product
  - Confirm
  - Receive payment
Typical cases when a product is sold
- Exchange of messages on messenger
- Offer on marketplace
- Either
  - Visit to each seller’s place by buyer or
  - Delivery of the product
- Payment either through
  - Cash or
  - Digital payments
- Product is marked as sold by the seller
I am assuming that we already have data of product marked as sold by the seller and data before the products were sold
Based on these data points, I will build a learning model to predict if the item is sold
Following are some of the features which will be most relevant (marked with a *) for this learning model will be
- Number of days it was posted
- Number of offers made
- Maximum number of messages exchanged on messenger *
- Number of people with whom messages were exchanged
- The content of the messages *
- The distance between locations of the people who had conversations about this product (Were they at the the same location at some point in between their conversations) (hard to get the data) *
- Buyer profile
- Seller profile
- Product category
- Product price compared to other similar products
Even after building a prediction model, I will make sure to get inputs for the model, by asking the sellers regularly if their product was sold or not.