Better tell that to Disney who invented the money swimming duck.It's not a liquid. It's a great many pieces of solid matter that form a hard, floor-like surface.
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Ever notice how some places don't accept American Express? It's because they charge a higher fee. That fee makes retailers unwilling to contract. In the case of debit being run as debit, the merchant may or may not pass on a service charge. It varies by merchant. When you hit credit, they pay fees just as they would with Visa, typically around 2.5-2.75%. If that goes up too much, you're less likely to see strong adoption. I really hate that practice.
The merchant is more likely to deny the service if the fee it too high (ie American Express) and less likely to absorb the see. So in that respect you're correct. The fee Apple charge will probably affect adoption rates.