When I look for help from a trainer, I want to see some kind of certification from a reputable organization that teaches minimally aversive techniques and some modern behavioral theory. Examples would be CCPDT or Karen Pryor Academy. If the person were also hanging out their shingle for protection dog training, I would want to see related certifications, such as GSSCC Helper Training. Additionally, I would want to see evidence that my trainer has titled dogs in sports related to my goals for the dog. Even if my goal is nothing but to have a well behaved pet that is pleasant to walk and doesn't jump on people, a trainer who has put obedience, rally, or agility titles on a dog has at least some skill in teaching a dog to mind its manners and stay on task in a stimulating and chaotic environment.