I was interviewed in April by the Chicago Reader about a horrifying situation about a dog trainer in the Chicago area arrested for animal cruelty. Read the article.
I was interviewed to get a the perspective about, as a positive reinforcement trainer, why I think other trainers use abusive methods. A lot of people don't think about the implications of who they hire to give them advice about the raising of their pet. Whether they think it is "just a dog" and you "just train it" or they just assume that dog trainers are screened by the state in which they operate, I am not sure.
Besides requiring a business license, dog trainers are not screened or regulated in any other way at this time. I don't think that this is critical because then it could open up all other kinds of questions. Who would do the screening, what would the criteria be, what types of training would be allowed, etc. But, what you can do is to screen dog trainers yourself.
Check references, check their training credentials, go watch them train if they teach classes. A bad trainer can give you terrible advice and really ruin the physical or mental well-being of your pet.
Dog trainers should be versed in learning theory, be members of organizations such as the APDT, attended seminars and trained with other skilled trainers.
Know what you are getting into, choosing a trainer is an important decision that can impact your relationship with your dog for more than a decade.