A thief running a scam like this will try 5-10 cards before moving on. Your average customer only owns 2-3 cards. We usually flag a user when when they get 3 declines from 3 different cards - and if it looks suspicious enough at that point, we hellban them.
You never wait for the chargebacks. If you get chargebacks, they cost you a lot.
You try to detect/block immediately - if a thief wants to check 10 cards in 5 minutes, you want to block him in the middle of it. And you immediately revert/cancel any transactions that succeeded so that you don't get chargebacks.