The problem there jollyrog, is that the supplier has no way of knowing what fees are involved until they know what payment method you are using.
So you have two options, apply the fees as a surcharge once you know what payment method the customer is using. Or increase all your prices by an average of said fees, so you can hide the fees from the customer.
The first method is the more accurate one, and fairer as it doesn't penalise those customers that chose to use a more economical payment method, however the second method is generally prefered as it prevents customers feeling like they're trading with Ryanair
