I've gotten ticked off with people like this before, where I l offer a very fair price to make a quick sale, and they go nickel and diming. When I let them know the deal, most accept the offer or depart graciously, but a few "special people" continue their chintzy ways in earnest.
I had a recent month-long negotiation like that where I was so irritated with their continually petty behavior, that I responded in kind. I deleted the name from all marketplaces, nulled the nameservers so they don't resolve, and plan to keep it this way for a year or two, mostly so I never encounter this blood-pressure-raising nitwit ever again.
If he wants it, he's going to have to hire a broker and pay a higher price. Either way, I feel great.