I used to teach for free... I had a good full-time job as a contract computer programmer at an investment bank, and didn't need to take money from my students for after-work classes a few days a week. Just not worth my time keep track of it. Doesn't mean I didn't provide good instruction, thank you very much.

Anyway, unless you can share some specifics, it's hard for us to say much. Even what style/school of karate these people claim to teach may be useful - some things are known made-up nonsense, and others are legit, though individual schools or instructors might not be. Alternatively, links to some video or promotional material perhaps - just a few seconds of video often makes it pretty clear if someone knows what they're doing.