See "Can I return items purchased with Authenticity Guarantee?" on here:
https://pages.ebay.co.uk/authenticity-guarantee-watches/faqs/

It says:   In the unlikely event that the buyer receives an item that is not consistent with the listing, the item will be eligible for a return.  In order for a refund to be processed, all returns must be sent to the authentication partner for verification (to check that the item is still in the same condition and has all relevant accessories, or that the item is not consistent with the listing) and re authentication before the item is returned to the seller.