I don't take classes because the teacher is someone famous. I take the class because the teacher is teaching something I want to learn. If I don't feel that I've learned what I came for, I ask lots of questions, or have a conversation with the teacher about what I really wanted to learn and what was missing from the class, or as a last resort, I would ask for a refund. (I've never had to go that far.) I've never met a teacher who wasn't willing to give me a few pointers or answer some questions.