I had the same concern. As a "regular guy", I don't even have the benefit of "work-related training", so I'm really in the dark. What I decided on was to focus on instructors affiliated with this site or those they recommend. I assume any yahoos will have been drummed out long ago. Additionally, I'm limiting myself to courses within driving distance of home to reduce cost (and financial risk) and to courses around the $200/day range. I may stretch that budget for special classes or those that are highly and universally recommended (thus reducing the risk as a customer).
Anyway, that's my strategy for minimizing risk.
Chris