I would also add : Look for a class where the trainer is in control. By tha,t I don't mean controling , but in charge of the situation ie dogs aren't allowed to interfere with others (I walked out on a class where dogs were tied round the outskirts of the room, unsupervised and allowed to lurch at any working dog passing by. At another despite being warned otherwise, a silly lady let her aggressive wheaten terrier off lead , causing a nasty fight with a labrador. The trainer was able to separate the dogs and calm everyone down. She banned the offending owner, with no refund, too )
Barbara, Monty, Joly and Teddy.