You might want to think twice before swiping your credit card. You could be racking up extra fees. New rules are now in place that allow retailers to tack on an extra fee up to 4% in some cases. It’s all because of a lawsuit filed by retailers. So make sure you check your receipts because stores have to let you know in advance when they’re charging you extra. But experts say chances are most retailers won’t make you pay the fee since it’s sure to make people shop somewhere else.