There should not be an interest fee for you if you pay off the balance in full every month. Secondly I will bet either obvious or hidden, you are paying those use fees that the places have to pay the card issuers. Some may just include it and hide it in the price and cost of doing business. Maybe the Amazons and Walmarts are big enough to be able to eat the cost of those fees.
No. In person or online, they charge a “processing” fee, for payment by card that covers their cost for accepting any credit or debit fee to them. I asked. My power bill can be paid from my checking account every month with no fee, automatically or manually.
I think that the dorm they moved out of had quite a few girls.