Tell him to return it for a refund.
"I regret you are unhappy with your purchase. Please return it for refund."
Don't say who will pay for shipping.
If he demands that you pay for shipping, tell him that he will have to open a Claim with eBay for you to do that.
Which is almost true.
"I regret you are unhappy with your purchase. Please return it for refund."
He may drop it right there because he doesn't want to be on eBay's radar.
"I regret you are unhappy with your purchase. Please return it for refund."
If he opens the Claim, send the return shipping promptly.
If he uses it and returns the item, refund.
Then Block him.
Don't get into an argument about the condition of the item at any point.
"I regret you are unhappy with your purchase. Please return it for refund."
Relist, with any appropriate changes, and get some of your investment back.
If what he returns is not in the same condition that it was sent, you can then Report it to eBay.
But don't argue.
Because.
