[zinxq]

At this point, it's a long evolved set of heuristics based on any available data. Some quick rules around IP, Country, and email provider gets you a fair bit of the way there. But like any heuristic system that evolves, tweaking can get you to something that's "good enough".

The next step would be an AI system (like the very impressive Stripe Radar (which admittedly is in a different context)) but we're not ready for that, nor would it bring us significant value over our current system. And again - we pipe things to human for things in the grey area.