The Humane Society suggests the following:
It's essential that the dog trainer you select uses humane training techniques that encourage appropriate behavior through such positive reinforcement as food, attention, play, or praise. Look for a trainer who ignores undesirable responses or withholds rewards until the dog behaves appropriately. Training techniques should never involve yelling, choking, shaking the scruff, tugging on the leash, alpha rolling (forcing the dog onto his back), or other actions that frighten or inflict pain.

Why choose a Certified Pet Dog Trainer?
When you choose a Certified Pet Dog Trainer, you can be confident that you are working with a professional who has the knowledge and expertise to make your investment in dog training safe, effective, and even fun! Certified Pet Dog Trainers have dog training skills as well as instructor skills to enhance the experience and success for you and your pet dog.
Certified Pet Dog Trainers have earned this credential by demonstrating their knowledge and experience in dog training. A Certified Pet Dog Trainer stays informed of current knowledge in the field and is familiar with the latest, most effective training techniques and equipment. A Certified Pet Dog Trainer adheres to a strict Code of Ethics.
The Certification Council for Professional Dog Trainers is committed to maintaining rigorous testing and recertification systems to provide dog owners with information to help them make an informed choice when selecting a dog trainer.
So the next time you need a dog trainer, look for a professional with the Certified Pet Dog Trainer credential. Your dog will thank you!
What about other trainer certifications?
Before You Get a Dog
Different Breeds Have Different Needs by Trish King
Before You Get Your Puppy -Ian Dunbar
Puppy
After You Get Your Puppy-Ian Dunbar
Average Training
Parenting Your Dog-Trish King
Power of Positive Dog Training-Pat Miller
Oh Behave! Dogs from Pavlov to Premack to Pinker by Jean Donaldson
Positive Perspectives: Love your dog, train you dog-by Pat Miller
Books on Why dogs do what they do
Culture Clash-Jean Donaldson
The Other End of the Leash -Patricia McConnell
Don't Shoot the Doggy Karen Pryor
Aggression
Aggression In Dogs: Practical management, prevention and behavior modification- Brenda Aloff
Multi-Dog Household
Feisty Fido: Help for the leash aggressive dogs by Patricia McConnell and Karen London
Click to Calm -Emma Parsons
Website
Here is a dog that we trained starting at 10 weeks old. Wrigley
Want to see what your puppy is capable of? www.puppyprodigies.org
Great site for all things dog! Full of videos, books and articles from top dog trainers. www.dogstardaily.com
For information on clicker training. www.clickertraining.com
About Clicker Training Position
Why Use a Clicker and not just your voice
Scientific Proof That clicker is more effective than voice
Statements released by the American Veterinary Society of Animal Behavior
Importance of Socializing Puppies (8-14 weeks old)