the fees don't belong to the commissioner though, they belong to you for using paypal as your payment service. stores have to pay a fee to credit and debit card companies to utilize their services; because of this they factor the cost of these fees into their prices. if they don't want to pay the fees, they don't take credit/debit.

that being said, it's fine if you're discussing a commission with a customer and charge them $5.50 or whatever to cover the fees. but if you charge them $5 and then say "oh hey you owe me 50 cents for paypal's fees," that's not cool