Stolen bikes and parts are indeed a major category of "lemons". I have, however, bought some second-hand parts which are clearly legitimate, i.e. credibly docu

Stolen bikes and parts are indeed a major category of "lemons". I have, however, bought some second-hand parts which are clearly legitimate, i.e. credibly documented and not stolen: - parts that someone has bought new over the net (often from abroad), and then found out that they don't fit their bike, and cannot really return - parts that someone has bought, tried, and didn't like or need them, even if they did fit their bike. Generally, these are shipped in the original containers and come with paperwork, which means they were not from a stolen bike. The stolen bike market is big here (north Europe), though. Or at least the number of stolen bikes is huge, though I wonder who buys them. (My son-in-law had his bike stolen, then a few months later spotted a similar bike for sale on a net site resembling Craigslist, and went to "buy" it inviting the police with him. He got his bike back but I don't think the thief got anything but a stern telling off by the police, so he's back in business.)