Conceivably, the funds could be sent to an address that they send to before. Very far from perfect... could work if it's a centralized exchange, one could depos

Conceivably, the funds could be sent to an address that they send to before. Very far from perfect... could work if it's a centralized exchange, one could deposit to the same address more than once (or maybe there's a time limit for re-use iunno). And no way (good?) way of knowing you were sending to your own account on that exchange, or somebody else's.