It is important to find trainers that understand how to work with fearful dogs. Anyone can call themselves a dog trainer, but it doesn't mean that they have studied the current literature on dog behavior. A bad trainer can make matters worse for you and your dog.
The Association of Professional Dog Trainers provides lists of certified trainers around the world. The Certification Council For Professional Dog Trainers also lets you search for trainers in your area.
Questions to ask a trainer
How would you describe the type of training methods you teach?
You want to hear 'positive reinforcement' or 'clicker training' somewhere in their answer.
What was the last training book you read? What did you think of it?
Do an online search and see who wrote the book and when it was written.
Who is your favorite trainer?
Names of well-known positive reinforcement trainers incude; Patricia McConnell, Jean Donaldson, Ian Dunbar, Pat Miller.
Avoid Cesar Millan enthusiasts (most professional trainers do not believe he's as wonderful as TV audiences do).
How long have you been training dogs?
Do you have experience working with fearful dogs?
Fearful Dogs