Or their merchant account. I think they disallow charging different prices based on the card type - there was a big blowup a few years back because retailers di

Or their merchant account. I think they disallow charging different prices based on the card type - there was a big blowup a few years back because retailers didn't want to pay the higher fees to accept debit cards, but had to because the debit cards had VISA or MasterCard logos and therefore had to be treated the same way as VISA or MasterCard credit cards.