https://www.ebay.co.uk/help/selling/fees-credits-invoices/selling-fees?id=4364#section2
Final value fees
When your item sells, you pay 10% of the final transaction value, including postage. We call this a final value fee. We cap final value fees so you’ll never pay more than £250 for a single item.
If your item doesn’t sell you usually don’t pay a final value fee. However, if you offer or reference your contact information to another user or ask a buyer for their contact information, in the context of buying or selling outside of eBay, we charge a final value fee for introducing you to the buyer. In this case, the final value fee is based on the higher of the fixed price, auction start price, Buy it now price, reserve price or the price identified between the buyer and seller.