I just wanted to add, that not only does it depend on the trainer, but also on the dog owner.
The trainers are there to provide help to the dog owner to train the dog. There are no miracles. I think I've heard some owners complain about training classes, when they didn't put in the effort themselves to train their own dogs.
And sometimes...maybe sometimes, it depends on the dog. Some dogs are more mischievous, some may have different strengths and weaknesses.
Maybe if you can go online and go with a trainer with higher reviews??
That would be awesome to have a therapy dog! I always think that it would be so rewarding to have that experience of helping others with a well trained dog!