The alternative, and this is not a nice way to go – let him raise a dispute and you’ll win (if they were as described) and he’ll have to keep them.
eBay offer buyers a guarantee that they’ll get their money back if unhappy so I think Paypal are always going to rule in the buyers favour.
You don’t have to refund the return postage if the buyer has changed his mind.
If it goes to a dispute and he wins, eBay/Paypal will refund him in full – the cost of the forks and the postage cost he initially paid you.
Make him send them back at his own expense and offer to refund him for the forks only, not the postage. That’s the only chance you have of the transaction not costing you anything as eBay will rule in his favour – they always do.