I lost a sale once on some Fluval 403 filter parts.
No big deal, cuz it was a small $10 sale.
Same thing, though. The person said they'd come by and then they never did.
Never heard from them again.
So what's the deal?
Were they
really interested, or just imagining they were?

If they were
really interested, you'd think they'd call and arrange another time.
So why the no show?
Call me crazy, but I have it in my head that some people are afraid, for whatever reason, to follow through. Maybe they have second thoughts about revealing a face to a name, thus blowing their anonymity.
Or maybe they are afraid of getting their head bitten off. (My avatar may look like I'm into head biting, but believe me, I'm not).
As for the ethical dilemma of juggling two or more interested parties at the same time.....I haven't posted enough exciting things for sale, so far, to have to face that....yet.
Not sure what I'd do, in that case, but I like to think that I would honor the first person and if they jammed, then contact the next in line, advising that the item was still available.
If the sale was a total loss, then swallow it, make a note of who it was that jammed (personal blacklist) and keep posting the item. Eventually, somone will come through.
Also, I totally agree with never announcing something as sold until the cash is in the hand.
Cheers,