It is not the straight forward

If someones pays you through Paypal using a credit card or bank account transfer then you will pay a % which varies acording on the amount but averages out at about 4%.

However if someone pays you from the balance they already have in their Paypal account then you do not get charged any %.

So it always worth checking with the winning bidder how they are paying if it is a significant amount.

And loads of sellers especially those in Europe still apply 4% premium on purchases, they just hide the small print at the bottom of the page with their postage rates