I had a friend who went to a McDojo for years. I tried to warn him repeatedly because everything I heard about the place was a red flag.
He kept entering tournaments and lost every bout. He was supposed to be a blue belt but kept getting embarrassed. None of the others from his gym did any better.
Took him years to stop going, and he's still not convinced it was a McDojo - but again, there was no info on the lineage of the instructor's black belt. When he asked, he was simply told "I learned from Brazilians" by the instructor.
Now a bunch of those Tiger Schulmann karate places are advertising MMA and BJJ lessons, and every little town seems to have a local "Action MMA" or "<City name> BJJ" - there's 4 of them on a 2 mile stretch of a single road.
Maybe some of these places are legit. Maybe some of the instructors are actually legit black belts and learned from a Gracie academy or something.
Maybe.
But all of them? Nah. No way.