I've run into similar situations a few times (not at HF) with buying from 'private sellers' online. I know how irritating it can be.
After some thought, my reaction in each case was:
"It's a good thing that I got my money back, and that I will not be dealing with this person any more. Imagine the hassles I would have had if there had been a problem in shipping, or if there was a problem with the item. In fact, perhaps the seller backed out because he discovered something wrong with the item at the last minute. No point trying to force somebody to sell me an item; there'll be another available eventually."