Funny thing is, a good way of making someone hover their finger over that button is to try to deposit any significant amount of cash to your bank account. One part of the system says "Use cash!", another part says "What is this cash? How did you get it? From whom? Did you give them a receipt? Can you prove that?"

If "the electronics" break down, shops usually can't accept any form of payment at all, because that would be illegal with their on-line cash registers being offline...