will he HAVE to post it back if ebay find it in his favor? surely he cannot hold onto the item and the money?
They advise the buyer to post it back with recorded delivery, once its back with the seller, which ebay can track as they ask the buyer to provide them with the tracking number they directly refund the buyer with the funds that will have been put on hold when the case was opened.
Its spelled out on here: http://pages.ebay.co.uk/help/sell/shipping-returns.html
In particular:
"Or if the buyer asked eBay to review a case for an item not matching the listing description, and we determined that the buyer should be paid a full refund, we'll put the case on hold for 10 days and ask the buyer to post the item back to you.
We'll ask the buyer to use tracking or a delivery confirmation number so that we'll know where the package is in transit, and we'll be able to confirm that you've received it.
If a case was opened and we have confirmation that you received the item, we'll provide a full refund to the buyer within 3 days that covers the cost of the item and original postage & packaging.
If eBay finds in favour of the buyer in a case, eBay may seek reimbursement from your PayPal account or other reimbursement payment method on file.
Note: If the item isn't returned to you within 15 days, and a case was opened, we'll automatically close the case.
Buyers are required to pay return postage, except for rare situations when a buyer and seller agree to another arrangement."