(Former fraud prevention research scientist)
(Former fraud prevention research scientist)
* put an error message "you are trying to use a card issued in X from Y, contact support"
* put a prefilled unchangeable field containing the current country
* signal an error on all fields when I insert something invalid (say, country and city) rather than only the zip code
* block the transaction before you validate my card
Because if so, you're better than what is currently available. If not, I'd be happy to understand what would be the downsides of doing these things :)
EDIT: also I realized now: you'd flag me if I put a non matching _billing address_ rather than if I use a card from abroad? That seems counterintuitive :)
If the credit card you are using is stolen, eventually the billing company will have to charge back your purchase. Enough chargebacks in a month and the billing company gets a HUGE fine. It is in their interest to err on the side of caution in cases where something like this occurs.