Just want to point out that in June the Supreme Court sided with Amex that merchants cannot steer customers to other cards when they actually accept Amex. They have to either accept Amex or not, none of this "we prefer" or "we'll give you a discount" type of thing. They can do that for cash or debit, but they are not allowed to give you a discount to steer you to Visa, for example (because it violates the Amex T&C, which the Supreme Court upheld as a lawful contract the merchant is entering into).
https://www.npr.org/2018/06/25/62331...antitrust-case