They should have a big sign by the door so everyone knows this before ordering. The wait staff should remind the customers. I did see a credit card only sign at a chick fil a the other day
I went to Taco Bell the other day (my idea of comfort food) and wanted to pay with cash. You would have thought I was handing them a live handgrenade. I was astounded at how panicky they became.
They had to go get a cup for me to place the cash in then I guess they took it somewhere to diffuse it. They then returned with my change which was placed in yet another cup and handed the whole cup back to me.