I used to buy ag and construction equipment at auction, go through it, make it new again and sell for a decent price and obviously make a profit on my labor. Several times I would have a machine pending and would receive a higher offer before first dude showed up. Instead of selling to higher bidder I would call first dude and tell him I had a higher offer. Let's say dude 2 offered $2k more. (Dude 1 be getting angry at this point in my call with him). But I'd tell him the machine was still his at the agreed upon price or if he wanted I would send him a check for $1k and sell it to the next guy. Had a few consider it, but no one ever took the cash they always wanted the machine.
Having been on the other side of that situation as dude 1 and have things sold out from under me after the deal was done is definitely irritating.