I had this happen in 2009 trying to buy a pair of cb400fs. Called the seller before setting out on a 2-hour trip with my truck to his place, "Are we still on for 1pm?" "Yep."
I previously got a commitment from the guy that his 'neighbor' was not going to buy the pair of bikes -- the seller had said "Don't try to talk me down, my neighbor wants to buy them" and I told him "Well until I see them in person I can't say if I think they're worth what you're asking."
I got within 3-5 minutes of his house after the long drive and he calls and says "My neighbor just bought them." Not wanting to make a scene with him and the neighbor, I said a 'prayer' for the dude and turned around.
Fast forward to 6 weeks ago. A seller advertises a near-mint-condition cb350 with 4200 miles for $250, deal included extra gas tank and side covers, starter motor, titled, on non-op so no back registration fees, a good deal. I call him and said can I drive over in about 45 minutes? "Well, I've gotten a ton of calls, but if you can get there that fast, okay."
I told him I wouldn't set out to drive over unless he gave his word he'd wait the 45 minutes and he said "Okay, sure, I'll wait 45 minutes."
I'm 5 minutes away and he calls and says "Sorry, one of the other people just pulled up in my driveway, it's sold."
I told him "Nope, you need to tell him that you're a man of your word, that you already agreed to wait for someone to show up who you know is driving over, BECAUSE I'M NOT TURNING AROUND, I'm coming to your house, I'll be there in a couple minutes."
After that 400f incident no way am I not making a scene. I could see the papers "man arrested and charged for aggravated assault during attempted purchase of a 41 year old $250 motorcycle." I didn't care at the time, but in hindsight it was a dumb move, who knows what can happen.
So I arrive at the dude's house 3 minutes later -- NO OTHER BUYER WAS THERE after all. I bought the bike. I didn't want to make the seller uncomfortable about the lie he told me over the phone just a couple minutes back, he had a real sheepish look on his face, he was clearly embarrassed.
Here's what I think happens in these cases:
1) the seller mis-prices the bike and when he gets overwhelmed with calls he gets greedy.
2) or the seller gets tired of no-shows and decides "first person who ACTUALLY shows up with cash gets it, no more trusting these people who promise they're 'coming over in an hour."
3) or another buyer calls and when the seller says "Sorry, someone's already on the way to see it" and the caller says "Tell you what, I'll give you $300 more than what you're asking"
and the seller is unethical.
However when you get a cool bike it makes you forget the aholes.