You know how it is when you are in a used shop. If you don't know specifics of the model you want you may find it and not know it. You know, the wrong barrel on a receiver, that type of stuff. How can I tell if I am looking at a Handi frame with a shotgun barrel on it. Can I tell by serial number on the frame, are there other markings to look for. You just don't know the history on stuff you find used. Is there a way to spot these differences in order to make a better buy or find a really good deal.