1. the trainer comments on your figure
Your coach can ask you what you want to get out of your workout. But he should not tell you the "right" answer by suggesting that you lose weight, gain weight, or otherwise change your appearance.
The coach touches you without asking or in an uncomfortable way.
"The trainer can touch the client, correct you, and show you how to do the exercises, but this should either be discussed before the class or he or she asks already in the process, "Can I correct you?" Ideally, the first option."
2. Exercises lead to injuries
Maybe you did the exercise incorrectly and it resulted in an injury, or maybe it is generally contraindicated to you because of your health. Either way, it is not your responsibility. You don't just pay for the service of a professional - he's supposed to know what to do. "Exercises that lead to injuries speaks volumes about the qualifications of the trainer.
3. the trainer allows himself insults or inappropriate jokes
There is a stereotype from TV shows of the noughties and programs on TLC about an aggressive coach who humiliates his charges and yells all the time on and off, motivating them in this way. But, first of all, this clearly has no place in the service industry, and secondly, it is simply a relic of the past. Communication with a fitness trainer should be comfortable and not go beyond professional activities. Remember that you set the boundaries here.
4. The coach drives you and "punishes" you.
Remember: you are not in the army, not in a sports school and not on a reality show. Therefore, phrases like "If you do not do ten push-ups now, you will do twenty" here is completely inappropriate. However, if you work with a specialist for a long time, between you have already established contact, the boundaries of acceptable jokes and you feel comfortable in the training, then perhaps there is no reason to doubt the instructor. As in all the previous points - it is important to listen to your own feelings.