I feel your pain. I paid for a 6 week course and dropped out on the second day because it was really awful.

And I agree with the others. Watching is important. Jot down any questions you can think of while watching, but you definitely want to go see the class in action. I didn't with that class and regretted it (granted, I didn't with the one I'm going to now, but she came highly recommended by someone who I trusted and had trained with before, so I wasn't that leery of going there).

Another little tip, at the end of the session you watch, chat to some of the owners out of earshot of the trainer and see what they think. If you like what you have seen and heard, then have a chat with the trainer and hopefully book your course.

Good luck with your training - at the right class, both you and your dog will really enjoy it