Couple of good articles from Grant Cunningham on finding a good instructor:
http://www.grantcunningham.com/2014/02/the-two-questions-your-defensive-shooting-instructor-should-be-willing-and-able-to-answer/...everyone has biases, and preconceptions about situations. Does your instructor know what his or hers are? Can they articulate them? (Note: no one is really good at identifying ALL of their biases. However, a good instructor should be introspective enough to know at least SOME of theirs.)
In addition, contrary to popular belief, sometimes things DO change in the self-defense world. If an instructor has never changed their mind about anything, that's....a bad sign. What have they changed their mind about, or learned and now do differently, in the past year or so? What have they learned in the past year about violence and crime, that might affect what and how they teach?
And then:
http://www.grantcunningham.com/2015/08/more-questions-you-should-ask-your-defensive-shooting-instructor-and-why/....if the instructor doesn't know anything about teaching, then how much do you think you are going to learn, no matter how good they might be at the technique themselves? How much COULD you have learned had you gone to an instructor who actually knows how to teach?
If you want to go someplace to simply be impressed by the instructor's skills, great. But if you are there to learn how to be good yourself, shouldn't you find out if the people can TEACH it in addition to do it?