You don't wait for actual confirmations when you are paying for a subway or a starbucks coffee you stupid idiot.
If I wanted to, I could open my banks app on my smartphone, buy a Starbucks coffee with that banks ATM card and watch the money come out of my account before they start making it.
I don't think you should be calling anybody a stupid idiot, know what I mean?
Edit: Not only that, I can always see on the POS terminal where a PIN is required the word APPROVED when making a purchase. If that isn't confirmation to the merchant I don't know what is.