Even with positive feedback, he can still open a refund request. If he does, you wont have a choice but to refund him AND you might get a defect.

Id just refund him and be done with it - but keep it professional - tell him he needs to return it in original condition first.

If he cant or wont return it, no refund. Thats how Ebay works (supposedly.. but he doesnt need to know that).

Many buyers on ebay have access to sellers home addresses / phone numbers. If they dont follow the rules, they still dont get a refund. If someone starts harrassing you, you report them to the police. But really, its unlikely that will happen.