[nine_k]

With ATMs and debit cards, I thinks it's generally not true, they seem to use the online mode and update the balance of a checking account within seconds.

With credit cards, you can indeed start more transactions against the same balance, and you're never sure in which order they will complete.

[KirinDave]

Gonna repeat, it is DEFINITELY possible to spend the same money multiple times with one ATM card, using old ATM machines with other payment methods.

No, I will not further detail how here.

[spooneybarger]

I can verify this is possible.

[nine_k]

Interesting! A bit or research in this area may literally pay :)

[readams]

you can do this but the bank will know and the police will show up.

[KirinDave]

I don't mean to endorse such behavior, but the folks who used a loophole after stealing my ATM card details from a data breach never got caught using a variety of ApplePay based variants of this attack (now fixed, btw).

In general folks who get serious about it never get caught. Which is why folks who give a damn about the world don't talk about specifics on public forums.

[erik_seaberg]

When a payment processing system doesn't promptly cancel auth holds, customers definitely complain about being prevented from spending their money. This stuff should be table stakes but some retail banks are just way behind.

[KirinDave]

That is the reverse problem. Flippin' gas stations STILL have a problem with this that you feel acutely because the large holds. A similar problem exists with hotels, where they'll put a lock on a ton of money in your account.