[bxio]

In my experience, some small businesses avoid Apple Pay/Google Pay because you can add American Express cards to them, and they want to not accept Amex cards in order to save on the fee, despite the service agreement of their payment processor obligating them to.

[Marsymars]

I don't think it's possible to have a PoS terminal that doesn't accept physical Amex cards but that does accept Amex cards via Apple/Google Pay.

[syntheticcdo]

A post-it note that says "American Express not accepted" is probably deterrent enough, rather than a technical solution.