Haha, picturing swap meet people wandering the streets in their free time just looking for people to offer ridiculous deals to, moaning "muuuuuuuust seeeeeeeeeell biiiiiiiiike paaaaaarts."

Would Mr. Sketchy go and grab them? I dunno. There are a lot of things in this story that don't add up but the sketchiness definitely outweighs the legitimacy. I say they're in all liklihood stolen. I don't think the OP should do anything about it. Ride them and use them, if he/she sees a "Stolen Wheel" flyer or something, I think then is when he/she should step up.