Before you add credit card surcharges, learn what the big players know — and how to protect your business from costly mistakes. Small and midsize merchants are racing to add extra fees to customers' bills to cover credit card processing costs. Surcharging means adding a fee at checkout to cover the cost of customers paying with a credit card. Keeping rebates: Most businesses are unaware that they should receive their processing fees back on returned or voided sales, and the credit card processor pockets those refunds. Related: How to Choose a Credit Card for Your StartupMy final thoughtsHow do you feel when you get surcharged?