I was a teacher for a manufacturers rep in New York for more than 10 years. I decided to go out on my own in 1989 and helping me make that decision was the fact that the classes I did for contractors in our conference room were always sold out. I attributed that to several things: I sort of knew my subject (learned out of terror because I once got up to teach about steam heating when my head was still mostly empty. Contractors can be brutal.) I was fun to be with. I had a lot of props and once even set myself on fire, but not intentionally.
We also charged for the class - not much but we did. We learned that if something is free it's also easy for contractors to sign up and then not show up.