The seller does not have to sell. Seller did not transfer goods to Ebay posession to sell it for him. Ebay is merely an agent here. Seller violated agents rules and thus have to pay final value fee that is all seller has to do. What if you refuse to sell your house after offer was accepted by you. You would pay comission to your real esttate broker and walk away from the deal. Same here. There's a contractual relationship between the seller and eBay, but eBay is not a legal agent of the seller, per eBay's User Agreement.