Nico's issue stems from the fact that when he did find something in his budget, het got shafted by a seller who 'got a better offer'. It's happened to me before as well, and as annoying as it is, what can you do? Taking them to the small claims court might be an option, but it's not like you can sue for specific performance if the bike has already been sold on. So you're suing for damages, but you need to then prove damages, which doesn't seem like it's worth the hassle.
Heck, I was once on my way to pick up a bike (arranged, agreed price, everything) in Joburg when I got a call from the seller saying that there's someone else at his premises willing to pay 20% more, am I willing to match it. I was stunned! I said thanks but no thanks and turned around and went back home. Ridiculous.
The rating system is also a contentious issue in my opinion. I'm a firm believer that it should only be used when an actual transaction has taken place to prevent frivolous ratings from being issued nilly-willy, but that makes rating these dodgy non-transactions impossible as well.