How disheartening that anyone has to go through such an experience. Training is supposed to be fun for both you and your dog, especially a class like agility. In a worst case scenario it should at least be informative and useful. The point is that a dog trainer needs to be good with people too, not just dogs. The two go hand in hand and unless you want to lose clients you need to have those people skills to be able to effectively communicate. If you turn off a client with condescending behavior it is going to drastically effect how you communicate with each other. This is a critical component when you are trying to teach new skills.
If you end up with a trainer you don't feel comfortable with feel free to leave the class, seperate from the group, or end the session. Speak to your trainer and let them know your dissatisfaction so they have the opportunity to fix the issue if possible. Perhaps they are unaware. You are paying for a service after all. Time is money and if they are wasting your time, they are wasting your money as well.
Remember, you are the only voice your dog has. Never let a trainer do something you are uncomfortable with to your dog. Trainers are not all created equal and some don't know as much as they should about dog behavior. (some stick to training only and don't bother learning about behavior information believe it or not)
Even with a great trainer there can be personality conflicts. Keep that in mind as well. If your options for training are limited you may have to tolerate a personality you don't particularly mesh well with. However that shouldn't mean you need to tolerate rudeness. If that happens to you do not hesitate to point out you are paying for their services and can look elsewhere. Not everyone who gets into dog training has the people skills needed to do well in the field long term.
Check out another post on the subject of people skills in training here: Dog Trainer...A Misleading Job Description by Cindy Bruckart
It is my sincere hope that the majority of training is a pleasant experience for all involved. Regardless of the methods taught or the type of class or trainer you see, it should always be a fun and rewarding event you share with your dog. Anything less is just plain unacceptable.