Never charge a fee. Mastercard and Visa forbid it. raise your prices 5% and then give a 5% cash discount. On one hand Square is the best thing since sliced bread. On the other hand the one downfall is they are not PCI compliant and you could be liable for credit fraud(were talking upwards of 50,000 for a fine.) When they first came out they claimed to be compliant but now the rules have changed to include mobile devices and until they change how the information transfers from the device into the phone there not compliant. Better off going with a company that is linked through quickbooks or whatever software you use, then use Trustwave for 7.99 month they will make sure your compliant.