Craigslist often has some great deals on older bikes in lightly used condition. But it also has ads from professional bike thieves. If an ad is form someone selling lots of cheap, more heavily used bikes that they made no effort to fix up, chances are good they were stolen from a college campus some distance away and taken to a different campus to resell. If your seller has a pickup truck load of such bikes, see if the truck has out of state plates.