Ran into a similar thing with a 4-wheeler I was selling. Was for sale for a couple of months with no calls. Then on a Thursday I got a call from a guy that said he could meet me 1/2 way the following Monday to get it and he seemed seroius so we had a tentative deal. Friday another guy calls and says he wants it. I told the 2nd guy that someone was supposed to get it Monday and I could call him back if it didn't work out. This guy tells me he wants it for the weekend and will come get it in the morning and asks about 1st come 1st serve kinda deal. I didn't want to screw the 1st guy over so I told the 2nd guy I would think about it. I tried to call the 1st guy back, left a message and when I didn't hear back from him a couple of hours later I called the 2nd guy back. I still have the 4-wheeler. In the future I will tell any potential buyers that the 1st guy to show up with cash in hand will take the item. I think if you have made a deal and someone is on the way it would be wrong to sell an item until after the buyer was supposed to be there but other than that 1st come 1st serve.