It all depends on the circumstance. If you had a shop, and someones car just happened to dissapear from said shop. and a few months later you magicly have the same motor or trans or whatever from that car in your shop. But it just so happens that it does not have numbers.. if you get a detective with a hair up his ass he could impound the car and have them try to retrieve the serial. ( which can be done if not properly ground off so i hear ). one way or another its not fun dealing with cops when you own a shop and your doing shady shit. they can just say "hey thats a chop shop". come in shut you down for the investigation. Customers wouldnt like there cars locked in a shop thats under investigation would they?