Yes but when you open a school you better be able to teach all levels. Or be prepared to turn away the students that are not beginners.Some people are rank chasers. He may be an excellent teacher, particularly for beginning students.
Well, while he was still with our master (1st master) he would still attend separate classes with the master instructor. That all stopped once he left of course. I know that he and his new master had a falling out due to differences in styles. He still considers his first master his master and teaches in that style. Now how is he to advances his own knowledge? He can't. Because he stepped on two masters, and one well known in the circles that be, he is pretty much black listed. There is no support and he is banned by most.My big question would be what he did about the material in those last three geub grades. If he learned the full curriculum and is a competent instructor, then I am not sure how much of a difference his being a rank chaser is.
Also his first master was a BB in a few arts. Judo, Hapkido, TKD. He only learned one art from this master. We only begin to learn these other arts once we become BB in the base of TKD. Only then do you get to study the other arts and those arts only enhance the TKD. There was just so much more to learn in both his TKD and the other stuff. I am still learning something new everyday and stuff that I though I knew I realize that I only know the surface of. Simple stuff am and finding out only now really how to apply it. Even something as simple as a punch teaches me something new each day. And SD is a whole other amimal. He knows his basics but that is about it.
All I can tell you is that he is hurting for his action. Yes he can teach beginners like you said but that is really about it.Now, knowing what you just said, I would not go into business with him. But that is a separate issue from his ability as an instructor.
Daniel