I know it's frustrating but sometimes, those tire kickers turn out to be buyers with a lot of money. Here's a case in point.
About three years ago, I had just finished building my third airplane and she was a thing of beauty, magazine cover, internet coverage, etc. One day this guy emails me about selling her. Same as you, it wasn't for sale, etc. I told him no. Two days later, he emails me again and asks if I was sure. By this time, I tossed out a ridiculous number just to get rid of him. He hems and hawas about the price and my response was "If you want my pride and joy, that's what it's going to cost." I figured that was the end of that. Three days later he calls me and asks when can he come pick it up.
I suspect that you (and many others) will face the same question over and over again. Just have a big number in mind and shoot it to them when they ask. If you get it, great. If not, who cares, it's not for sale.
Sometimes miracles happen.