The following is an excerpt of our upcoming book on dog training..

If you are the kind of person that is motivated enough to find and read this book you have probably researched dog training at least a little bit. Enough anyways that
you have probably read several different methods that swear up and down that they work and that the other way is abusive, cruel, useless etc. If you are not a professional how do you sort the wheat from the chaff? When I first became interested in dog training I had the same dilemma. The simple answer I found is results. Not anecdotal but actual visual observable results. When this becomes your criteria the field narrows considerably. 
Here are some questions you should ask yourself when selecting a trainer and or training method to follow.
Probably the first and most important. Do they even have success in the training area you need help in?  Perhaps the agility champ trainer with her super fast Border Collie or the Doggie Dancing competitor with his Australian Shepherd isn’t going to be very helpful when dealing with your aggressive dog or helping you with your dogs street obedience. Make sure the trainer you select has actual success in the field you need help in.
Have you seen dogs that they have trained? Have you seen a body of work, aka several dogs that come from their system? Is this something you want for your dog? In this internet and smart phone era do they have video of their work and results? A dog trainer that does not have a video portfolio in this day and age is probably a dog trainer with something to hide.
Here is my basic test of competence for any dog trainer. If they can show me a dog, preferably several dogs they have trained OFF LEASH preforming reliable obedience in a busy public place under distraction without constantly baiting the dog with food, toy or playing the look at me game (A sufficiently motivated dog can be baited for a few minutes to look good on video); then they are worth looking at as a companion dog trainer. If they cannot do this simple thing, do NOT waste your time.