What you say is entirely correct.
EBay's money back guarantee policy is to support the buyer unless they can determine that the item matched the description.
As eBay itself is reported to have stated "As we didn't see the original item that you sent to the buyer, and we didn't see the item the buyer returned to you, we are not in a position to take sides in these situations and verify who has the valid complaint". When this happens, eBay applies its default policy, to support the buyer.
Yet if the seller disputes the case, and loses, they are penalised with a defect on their account and forfeit any return of fees. In other words, even though eBay doesn't KNOW that the seller was at fault, and may only have found in the buyer's favour because they can't determine blame, they will still penalise the seller with an account defect simply for trying to explain their side of the case.
A you rightly say, this is contrary to the principles of justice in any UK court. But this is what happens when a company takes it upon itself to adjudicate on its members financial transactions, without being regulated or supervised, and with members having no right of appeal to any independent authority.
