The real problem is that fraud is so rampant that there is just no way any more to tell. Some of the most well known "experts" in the U.S., (especially on forums) are frauds themselves. Even respecetd publications have been known to prop up fakes and discredit good people.
Anymore, you students just have to find a school that they like and go there with the knowledge that most of the competing instructors in the area will say that teacher is a fake.
The best thing to do is just stay away from commercial schools in general. Look for someone that teaches out of thier home, a community center or other non-profit place.
Never sign any kind of contract.
One of the best things that "legitimate" schools can do is do away with the ranking system. If there are no ranks, there's no way to sell ranks and then there's no way to be accused of selling rank. Which has been happening since the very start of it.