I applaud your patience in this situation, OP. I think I am a little more jaded than you are when it comes to online selling
I would have told the guy to take a hike pretty early in your scenario, haha.
As others have mentioned, you learn to weed out the crazies. I actually buy and sell on Craigslist fairly regularly. There is an art form to it, I think. Lots of idiots out there, and they vastly outnumber the serious buyers. It really makes you wonder about the future of our nation(s)