Now, in my experience with NAUI technical diving training and two other agencies, NAUI is the most difficult and hardest to get. In fact, other agencies, including big name ones, are easy to become tech instructor let alone technical diver.
As for knowing a bad cave diving instructor, I never said that they don't exist in any agency but it is much less so with NAUI. I am speaking from my personal experience across 4 continents. You wouldn't believe the crap taking place near and around me (with agencies not NAUI). I am very active in the region and I see most horrible crap with other agencies in technical instructor training. Give you one example, I know for fact and personal first hand knowledge a person who was NOT a certified DIVER by any agency in the world at any diving level went to a diver training course and at the end of the 5 day course, he was certified as a diver and INSTRUCTOR!!! I know the guy very well and know who "certified" him and know everyone involved. This is one example in addition to my own personal experiences. You can criticize NAUI all you want for other reasons, I may join you too, but not for their standards and their QA. If I want to take a technical training course, I'll have no issues or second thoughts about doing it with any NAUI instructor but I have to do my research and investigate before hand if I take it with another agency's instructor. As I said earlier, there maybe bad apples within NAUI in technical training but they are going to be extremely rare in contrast with other agencies. Again, I am speaking from personal experience.