Marketplace trust + fraud prevention from day one
How to design trust into a marketplace before fraud becomes a customer-acquisition tax — the controls that prevent both sides from gaming the system.
Marketplace fraud is the silent killer most founders don't model until it's eating 10-15% of GMV. The trust-and-safety surface you build in year one determines whether the marketplace scales or collapses under bad-actor weight. Here are the controls that actually work, by category.
The four fraud surfaces
Identity fraud — fake accounts on either side. Bots inflating supply, fake buyers running chargeback schemes, sellers with multiple accounts to game ratings.
Transaction fraud — chargebacks after delivery, payment fraud, money-laundering through the platform.
Reputation fraud — fake reviews, sockpuppet 5-star accounts, review-trading rings.
Disintermediation — supply and demand exchange contact info on the platform then complete the transaction off-platform to avoid fees.
Each requires different controls.
Identity fraud controls
- Phone verification on signup. Cuts bot signups 90%+. SMS verification via Twilio, Vonage, or any major provider. Trivial to implement; massive deflection.
- Stripe Identity or Persona for higher-value sellers. Government ID + selfie for sellers above a transaction threshold. Cost is real ($1-3/verification) but the fraud savings dwarf it.
- Device fingerprinting. FingerprintJS, Castle, or Sift detect when the same device creates multiple accounts. Critical for catching multi-account rating manipulation.
- Email domain rules. Block disposable email domains at signup. Most fraud accounts use them.
Transaction fraud controls
- Stripe Radar (free, on by default with Stripe Payments). Catches the obvious patterns. Tune the rules as fraud patterns emerge in your data.
- Holdback period on payouts. Don't release funds to sellers until 24-72 hours after delivery confirmation (longer for high-value items). Stops the "deliver-and-chargeback" pattern.
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