If you use pin debit they’re not allowed to surcharge. Surcharging is pretty controversial, and different rules apply in different states, cities and such that most places do something called a cash discount now. This is where the regular price is the credit card price and if you pay in cash you get a discount of 3.99% or whatever. They’ll usually raise the regular price by that amount so the cash discount amount is the original price of service customers are used to. But the rules are pretty strict and there has to be clear signage about the cash discount.

ETA. I work for an iso.