My dad's 1st cousin has been in martial arts 40+ years, has been an instructor, coach for instructors, movie consultant - you name it. He feels very strongly that way too many martial arts instructors are clowns and are devaluing, or corrupting, martial arts practice. So yes, sometimes the stuff in strip malls is good, but many times its not. If they're promising that you'll get your black belt definitely in <3-4 years, or, conversely, if you have to practically die to get it (starvation, sleep deprivation, fighting a room full of black belts, and then be evaluated afterward), then it's not legit.
Is that your experience? Stuff your Dad's cousin has said and maybe not even directly to you? Have you ever been involved in karate yourself ( yes/no) circle one.
Yes there are certainly very weak Teachers who run Karate Mills. You have to be careful and get some advice before signing up.
While starvation was not part of the Black Belt Test ( I have either participated in or watched dozens) fighting everyone in the Dojo is normal fare. You must demonstrate that you know all the forms from 1st to last, answer questions and then spar with everyone.
I remember one test in particular. The student was a very nice guy but maybe thought a bit too much of his own skills. So the Teacher brought in a ringer from New York who was in our association of Goju Ryu, a tall lanky chap.
Once the student had gone through all the others and was tired the Teacher had him fight the ringer who kicked his a.. very thoroughly. There was blood all over the mats. The teacher flunked the Student even though I thought he did well enough. He wanted to teach him a lesson in humility.
That's good enough for normal people leading a normal life. Once again, starvation or being left on an ice flow for a couple of weeks only takes place in the vivid imagination of folks who have not had much contact with Karate. God rest David Carridine.