Since your policy is already clearly stated, anything you do is "above and beyond."

Often, this is a trick on eBay to get money off, and it's "no risk" to the buyer, who has nothing to lose by trying it.
Call his/her bluff by asking them to return it at their expense, and you'll check it out, refund the money if necessary.

DO NOT issue a refund until it arrives back to you. Ask them to send it with tracking or delivery notification.

Chances are you'll never see it, and you can tell eBay you offered and he/she wouldn't send it back.

If it does come back, and it's messed up, you can refund and feel good about it.