I haven't used the seller part of my eBay account for ages, but the base PayPal fee used to be 4%. They effectively take commission via the currency exchange rates too, so it's not out of the question that your seller would be 6% down.

There can be quite hefty charges (at both ends) to transfer from a UK account to a European - one option if the seller is insisting on a bank transfer would be to negotiate them paying all bank transfer charges? They would still end up with more than if you paid by PayPal and you wouldn't be more out of pocket than expected by having to pay bank charges.