I dont go to stores that place a minimum or charge a fee for CC. Especially when they charge a fee, or are charging more for gas. A business having a credit card is not required but is a luxury for the business. With that luxury comes cost. It is a cost of business. If they have a problem with the charges, stop accepting CC's and go back to cash only, then see how slow your business becomes.
There is sub shop that I used to frequent near my house, the last time I went there were signs stating that there is a .35 fee for CC use. I refuse to go back there unless I have cash which is rare. Imagine if they didnt accept CC's, how many people would not go there. They have lost my business.
The CC brings people into the business, it should already be factored into the price, as well as the electricity bill, or marketing costs.