People selling stolen goods on craigslist almost always use a bait and switch scheme. They will list one item, and when they get a response, they'll say, "oh I sold that bike, but I also have this very similar one for sale..."

but I guess you could programatically account for that if you were truly so inclined.

The people selling stolen bikes often don't put much information, so you'd get lots of false positives.

All you need to do is look for bikes that are being sold for far less than their fair value

Instant CL TOS violation and would get you C&D'd. There have been stolen-goods-finding sites shut down by CL for less than that ...