Search and Moderation on a Two-Sided Marketplace: Fast Without Being Fraud-Friendly

Two-sided marketplaces have a structural tension: the side that lists wants zero friction, the side that browses wants trustworthy results, and an admin approval layer sits in between slowing everything down if you're not careful about where you put it.

Moderation without a queue everyone hates

The naive approach holds every new listing for manual review before it goes live. That kills seller experience — nobody wants to list something and wait a day to find out if it's approved. Instead, we let listings go live immediately and run automated fraud-signal checks in the background, only pulling a listing for manual review when it trips a specific pattern (duplicate images across accounts, pricing far outside category norms, brand-new accounts posting high-value items).

Search has to survive real browsing patterns, not a demo query

Search that works fine with a thousand test listings can fall over once real users start filtering by five attributes at once at real traffic volume. We indexed specifically for the filter combinations users actually applied — pulled from real query logs, not assumptions — rather than a generic full-text index.

The result

Sellers list without waiting, buyers browse without lag, and the fraud that does slip through gets caught by pattern detection instead of a human reviewing every single post. Moderation and speed stopped being a trade-off once we moved the moderation logic off the critical path.