Unless you live in California, Colorado, Connecticut, Florida, Kansas, Maine, Massachusetts, New York, Oklahoma, and Texas, where it is currently restricted to charge consumers an extra surcharge on transactions, keep your eyes on your credit card statement for “checkout” fees. The fee can be up to 4%.
Source: http://news.yahoo.com/retailers-may-begin-charging-swipe-fees-credit-card-155919028.html
The Cohenization Project 