Furthermore you can get into trouble over time. For instance you sell a few parts and later you sell the remainder of the parts. Because the statue of limitations if 5 years, they can get you for possession/sale of a complete machine gun, during that 5 year stretch.
I know a couple of dealers that bit the dust over a period of time.
Another way they can get you is to tell you all they need is one part to complete the M2. You sell them that one part, and you have now made an illegal transfer of a machine gun and go to jail without passing go.
I stay away from all that stuff, want nothing to do with it.