[GoldenAge50s]

I like David J's idea!

This is what I would do: He is also an eBay seller himself. He currently has 136 items for sale. I would tell him that if he leaves you negative feedback, you will use one of your other eBay accounts and buy an item from him and leave him negative feedback as well.

Even if you don't have another eBay account, he won't know that. He knows can block you as a bidder now, but he won't know the user id(s) of you other account(s) to block. It will probably keep him from leaving you negative feedback.