Yes but who can prove what you are doing? In my business no two people pay the same amount for the items I sell. So I can just tell the customer who uses the high fee credit card that the price went up due to fuel increases. I don't tell them it's because of the credit cards. And since it is mostly government employees they don't care what it costs because it's not their money they are spending. As long as the sale is under the limit of the card they'll just charge it.
They always tell me their card limit so I know what to charge.