I am going to try to give an honest opinion hopefully without offending anyone too much, but the truth does sometimes hurt.
1) Hank Haney has instructed students who have won every major championship in golf. This accomplishment goes a long way in producing credibility.
2) Becoming a world class player yourself goes a long way in producing credibility. If a player like this tells me something then I will consider it much harder than say if a c player instructs me.
3) Now when someone plays at a b level tops and has never produced any great players goes to chirping about being a master instructor, they don't receive the same credibility from me as the ones who have done more to earn their credibility. Then when the instructor preaches that pros cant teach. They lose all credibility in my eyes.
I personally have seen a "good" player mentor a player who became great so I know there are those who can teach better than they can play. I am not going to say that is untrue. But that good player really knew his stuff.
I have also seen some good players go on the road with great players and the great player did in fact teach the good player to become great, so I don't buy into the players cant teach philosophy either. The pros know what does what when stroking a ball and they know the mindset needed to win and they know the strategies to get there and all of those they can and have taught. Maybe a guy like Shane is not as well spoken and a "professional instructor" can use that as a way to market himself as being the guy you want to come to if you have a question, but I know if I had a question I was searching for an answer to and I had access to both Shane and the "professional instructor" who can not play and has never taught anyone how to play world class, I'm going to Shane for my answer. He is the one I trust knows the correct answer.
I have never heard an instructor on here say that pros can't teach. I have heard them say many times that just because someone plays at a pro level does not necessarily make them a good teacher. It takes a certain skill set to be able to teach effectively, and not everyone has that. I have also heard the same people list certain pros who they thought were very good teachers.