Compliance and law
Source of funds
Evidence of where the converted amounts came from, required above certain amounts.
The request is for concrete documents: a statement showing the original purchase, a sale contract, a payslip, a notarial deed. It is not an individual suspicion: above certain thresholds it is mandatory, and its absence blocks the operation.
A second, separate check covers the on-chain origin of the deposited assets. It can produce false positives, since an address may have received dubious funds several hops upstream without its holder knowing. Manual review exists precisely to separate those cases.