This is a generality but fraud requires that a false statement be made – knowingly – with the intent to induce reliance on it. There is absolutely nothing fraudulent about a homeowner withholding better offers in a short sale situation. Now if the bank specifically inquires regarding other offers and they are told no other offers exist, that is probably fraud – a false statement being knowingly made to induce the bank to accept a lesser offer, which arguably damages the bank.
The fraud accusation is something that gets thrown around in the blogosphere quite a bit and in a cavalier fashion. I would estimate that 95% of the fraud allegations that I see in cyberspace are not fraud, and not even close to being fraud. It’s a word that many use without understanding what it really is. No offense intended to anyone, of course – just my observations.