Buyer claims the item has missing parts! What now?

I sold an item and the guy took forever to confirm it.m, however, he is accusing me of having taken a part of the item. I haven’t and I’m fairly sure it was in the pocket, but I don’t have any proof. He wants to return it.

I’ve never had issues before and I have full 5 star reviews. I don’t know how to deal with this. Any suggestions?