Safety, safety, safety, safety.
CrossFit gets a bad rap because people get hurt. It doesn't have to be that way, but people get so caught up in the competition and the no gain without pain/sweat angels/pukie the clown attitude and proper form goes out the window. I can hear tendons and ligaments ripping from here.
Become obsessive about proper form, WOD scaling and crawl/walk/run/sprint. Clients need to earn the right to train with high loads and/or intensity.