Maybe this might clear up any confusion. Below is part of the user agreement wih PayPal. Most credit cards have similar agreements.
4.6 No Surcharges. You agree that you will not impose a surcharge or any other fee for accepting PayPal as a payment method. You may charge a handling fee in connection with the sale of goods or services, as long as the handling fee does not operate as a surcharge and is not higher than the handling fee you charge for non-PayPal transactions.
In other words you are not alowed to pass the surcharges or fees on to the buyer for using PayPal or credit cards. Those are fees that the merchant gets charged for the convenience of using PayPal or credit cards. Same with the buyer, they get charged their own fees, usually as interest for using the same services.