My "gym" is quasi crossfit as well and I have no qualms telling the trainer "no". I do worry about people who aren't assertive enough to trust their own bodies.
To give the owner credit he will have us take an entire week and have us use very light weights to focus on form, usually once every 3 months.
The people I worry about are 1. my friends who use CD's and work out at home - no one is watching their form and 2. just heard of new gym in town where they make their own kettle bells using duct tape and sand bags and finally 3. the non trainer who shares their exercises with their friends - again one of my bike buddies is telling me about a kettle bell exercise where you swing the ball up and over your head - yikes.