From personal experience the places where it is cheapest to buy stuff, only accepts cash transactions. Talking to one store owner it is because of the credit card company’s cut.

I was surprised at how high the fees were. For instance, in this example of a Mastercard, when you buy a $1.50 pack of gum at a convenience store, the credit-card company gets 28 cents. Even on big-ticket items like airline tickets, the credit-card company collects nearly 3 percent.

This is not to say that there is anything wrong with those fees. I presume that the issuing banks can choose their own fees (within reason), and that there is more or less free entry — which suggests that the industry should be pretty competitive. Merchants accept credit cards, which implies that the benefits of doing so outweigh the costs.

The True Cost of Credit – Freakonomics Blog – NYTimes.com.