Merely dismantling non-crashed aircraft and selling the parts in 'As removed' condition is not illegal. It's when something is then declared to be new, or overhauled/repaired/tested that it's fraud, unless the part has been through a repair shop. It would then have a Tag from that shop. It's up to the buyer and his Quality Control procedures to pick up on that. Most times, it's easy to tell if a part's removed from a 'Teardown' aircraft, because of the physical condition (Dirt in crevices, witness marks where bolts have been fitted, etc, etc.)
Moral is, buy from a known supplier with a good reputation, and insist on knowing the part's history. Any reputable supplier will be happy to do this. Half the problem with Suspect Unapproved Parts (SUP's) is that the FAA would not get involved for many years, their view was that it was a criminal matter, and therefore in the hands of the FBI. Our own CAA was approached by many parts suppliers, asking for some sort of accreditation scheme, but this has fallen on deaf ears as well.
The whole spare parts industry is a lot cleaner than it used to be, but it goes to show that it's still possible for criminal activity to take place. Buyer beware!!