Originally Posted by
mazdaspeed
I would try to outbid the other guy if it were a really high end bike, then report it (say you found it) to the police department assuming that someone would have reported it stolen and they would probably happily pay you back for the bum's crack money (I wouldn't pay more than like $150 no matter what the bike just because I wouldn't want to potentially lose the money). On the other hand if nobody reported it stolen it's yours to part out on ebay or keep

I like your way of thinking mazdaspeed. However, the OP provided no evidence that the bike was stolen! Most homeless people aren't crackheads, not that being homeless or a crackhead should give people the right to accuse a person of theft with no evidence. I agree that the whole scenario is questionable, but I wouldn't get involved without better reason for casting blame.
There are a lot of underprivelaged people around where I live that ride bikes. I am sure if one of them was in a jam for money they would sell their bike for a relatively cheap price. I'm also sure that some of those bike were stolen from someone at some point during the bikes life. That doesn't men that any time a less well off person sells a bike for a pittance the bike is stolen.
Even if the bike was stolen how likely do you think it is that it will get back to the original owner? I imagine most bike theft isn't even reported to the police. If the bike is confiscated and then no previous owner is found, then what? It all seems like a bad idea unless there is more evidence that the bike is stolen.