While I agree that some players are trained by illegal farms, it would have to be treated as a case by case and sorry to say, but that is not always easy. Imagine someone buying a player from another NT, then obviously cheating to get caught. Suck to be the other NT team, losing that player. Risk of sabotating is why there is some farms, legal or not.Between that example and Trainerman example will be several layers of "should we or should we not".
From the BBs point of view, they have to look out for everyone.