I see paypal charges as "cost of sales" and so don't charge for people paying by paypal
I will knock a bit off if someone sends me a cheque, but paypal is actually more convenient to be honest.
Every shop, pub, website etc incurs charges for having the convenience of taking payment by credit card, you don't get charged extra for using your card but you may get a discount if you pay by cash.
Just my sixpence worth
Paul