A buyer finds a listing, messages the seller, and asks one clarifying question. Three replies later, someone writes ‘easier if we just text’ and drops a phone number. The deal still happens. Your marketplace just isn't part of it anymore.
That's the moment every marketplace founder eventually watches happen, usually right around the time growth starts looking good. Chat gets scoped as a nice-to-have - a way for buyers and sellers to ask ‘is this still available’ and it ships as generic messaging. Then the take rate doesn't match the traffic, and nobody can quite say why.
Chat looks like a feature. On a marketplace, it's the transaction.
The Transaction Wearing a Chat Bubble
In most apps, the conversation supports the product. On a marketplace, the conversation is the product moment where trust gets decided - is this seller real, does the item match the photos, will the money and the goods actually show up on the same day. Get that conversation wrong and you don't lose a message, you lose the deal, the commission, and often the user's next visit too.
Three problems make marketplace chat its own category. None of them are about message delivery.
The WhatsApp Tax
This is the one that shows up on every marketplace's P&L, even if nobody's labeled it that way. A phone number, an email, a ‘find me on WhatsApp’ - any of them, and the transaction that was about to generate a take rate now generates nothing. It's not always bad intent. Plenty of buyers and sellers do it out of habit, because texting feels faster than an app. The outcome is the same either way: you built the discovery layer and someone else got the transaction.
Catching this reliably means reading for contact information in its many disguises - spelled-out numbers, spaced-out digits, ‘call me on the app that starts with W’ not just scanning for ten consecutive digits. Playo, a sports-booking platform, ran into a version of this directly: users were booking courts through the app, then jumping to WhatsApp to actually coordinate the game. The booking happened on Playo. The relationship didn't and that's the same leak a marketplace feels, just wearing a different jersey.
‘Scroll Up’ Is Not a Process
Eventually a buyer says the item never arrived, or a seller says it did. Whoever resolves that dispute needs to reconstruct what was actually promised and asking a support agent to scroll through the thread is not a system, it's a hope.
What you actually need is message history that holds up: who said what, when, with edits and deletions logged rather than silently overwritten, and enough structure that a support agent can find the relevant exchange without reading four hundred messages about shipping estimates. Quoted replies help here more than people expect - a dispute is usually about one specific claim in one specific message, not the whole thread.
Trust, Decided Before You Notice It Happened
Buyers decide whether to trust a stranger's listing in the first few exchanges, and that decision is made faster than most product teams design for. A slow reply, a message that looks like a scam template, an account with no history - any of it can end the deal before it starts. The chat layer needs to carry signals of legitimacy, not just text: presence, response time, verified account status, and content that's been checked before it lands, not after someone's already reported it.
The Part We've Already Built
None of this is exotic - it's just easy to underscope when chat gets treated as a checkbox instead of the transaction layer it actually is.
CometChat's AI moderation catches contact-sharing and off-app steering before the conversation leaves your ecosystem - platform circumvention is one of the essential rules built into the Marketplace/Classifieds preset, alongside contact details and email filtering. Data masking keeps phone numbers and emails from landing cleanly in a message in the first place. For disputes, messaging webhooks - sent, edited, deleted, read give you the audit trail to reconstruct what actually happened, and threaded replies keep the relevant claim attached to its evidence instead of buried in scroll. Ambiguous cases route to a human on a review dashboard rather than getting auto-resolved by a rule that doesn't have the full picture.
Marketplaces running this well see it directly in the numbers: platforms using AI moderation and in-app communication built for the category report meaningfully higher transaction completion and user retention, because the deal and the trust that makes it possible never has a reason to leave the app.
The buyer-seller conversation is the one part of a marketplace that's easy to build badly and expensive to have built badly. CometChat handles the moderation, data masking, and message infrastructure this piece walks through, so your team can spend its time on the marketplace instead of rebuilding chat safety from scratch. If that's the part you're staring down, talk to us - that's the part we've already built.
Shrinithi Vijayaraghavan
Creative Storytelling , CometChat