A guy my brother knows is a frequent target of the BATFE because he testified as a gunsmith at a trial of a man accused by the ATF of owning an illegal machine gun. The ATF fought him tooth and nail to stop him from disassembling the firearm and showing the jury it was literally broken. To this day they send straw purchasers into his shop.
A couple of years ago, they sent a guy in to sell his deceased father's M-14. Guy takes it in the back for a closer examination and saws the receiver into three nice pieces, puts the "parts kit" in a nice box and returns it to the idiot. Guy explains to informant, it was completely illegal to own and now it is completely legal. Reminds informant he should be thankful for the help and asks him to leave the store with his new parts kit.
Informant drives away, five minutes later ATF agents from around the corner come into the store pissed that their bait gun was destroyed and rant at Guy about the loss of their "borrowed" property. Guy apologizes, reminds them informant was wired and they heard what was happening. Guy asks them to call and warn him next time so they can avoid similar events in future. ATF leave and still harass him, just not with the old, "I found Daddy's machine gun trick".