Unfortunately, there are some gun wise people who will make illegal conversions for money. Those are the guys I hope BATF nails to the wall. As far as maybe doing the conversions themselves, just because someone is a crook doesn't mean he's stupid.
There have also been reports that some Chinese selective fire AKs were brought in for sale to criminals. Supposedly, these were brought in by "gun runners." Maybe, but I can't see a totalitarian government not noticing that thousands of automatic weapons were missing. Perhaps the Chinese government was given the green light in return for favors elsewhere. When some customs agent who didn't get the word caught them, everyone blamed the "gun runners", the right wing conspiracy, and the NRA.