Well, Paypal gives the impression to buyers that they're the ones telling Paypal how much to pay anyway. If I recall correctly the amount displayed on the Paypa

Well, Paypal gives the impression to buyers that they're the ones telling Paypal how much to pay anyway. If I recall correctly the amount displayed on the Paypal payment page is for information only and the API leaves it up to the seller how much to actually charge, and in some cases this may change (for example, because the site can't calculate shipping fees until Paypal gives them the buyer's address).