Guys here's my opinion
Joe Blow buys a 100% receiver (the firearm). Joe add parts to the ALREADY FFL registered firearm (the receiver). Now one day Joe says, "hey, I need money for groceries, cigarettes, hookers whatever". He sells the ALREADY FFL'D professionally manufactured receiver that has the serial number on it to Bubba.
Is Joe Blow a gun dealer, a gun manufacturer? I hardly think so. Is JOe engaged in the BUSINESS of making illegal guns? I don't think so.
I think Joe should build HIS GUN on the FFL'd Receiver and then sell it later if he wants money for something else. A one time, two time, three time sales of a ALREADY FFL'd guns hes' built is no big deal in my book.
Now if JOe were actively engaged in seeking out customers, custom building or even had a small production line then this is a whole different story.
Last comment - YES the Govt has all the power and YOUR money to screw over Joe all they want to -even when they are wrong. But I think they have better things to do than screw with Joe.
Shoot, some of you guys have enough home builds to arm a platoon - so you sell a few off in casual sales. Does that make you a DEALER, a manufacturer? If so, close down AR 15 Builders forum, we are all going to jail for not keeping every gun we ever worked on.
My 2 cents - discounted today only 1 cent.