Marketplaces
Two-sided trust: a bad seller costs you more than a bad buyer, and both arrive as ordinary signups.
What the problem actually is
A marketplace's product is trust between strangers. Fraudulent sellers list goods they do not have; buyers run friendly-fraud chargebacks; and both re-register the moment they are banned. Enforcement without identity signals is a treadmill — you remove an account and the same person is back within the hour under a new email.
Signals that carry the weight here
Ban evasion is the defining marketplace problem, and the device is what a banned user is least able to change.
A value first seen across the network days ago and already flagged elsewhere is worth knowing about before it transacts with you.
A brand-new domain behind a seller account is a common pattern in listing fraud.
Where to start
strictness=2 (strict) — Strict for sellers, balanced for buyers. The asymmetry is deliberate — an abusive seller damages other customers, an abusive buyer mostly damages you.
A defensible starting point, not a guarantee. Strictness moves the verdict thresholds only; the risk score itself never changes, so you can re-tune without re-scoring anything.
The call
curl -X POST "https://www.layercall.com/v1/score/user" \
-H "X-Api-Key: YOUR_KEY" \
-H "Content-Type: application/json" \
-d '{"ip":"$IP","email":"$EMAIL","device_id":"$DEVICE_ID","strictness":2}'1,000 lookups a month free, no card. Get an API key.
Questions
Does the device fingerprint work if they clear cookies or use incognito?
Yes. It is computed from characteristics of the browser and hardware — canvas and WebGL rendering, fonts, timezone, screen — not from anything stored on the machine. Nothing is written, so there is nothing to clear.