Piggybacking off a post during the final weeks of December about deciding to be great at one maybe two things and punting all else; I'd like to elaborate around the context of Personal Training.
As a consumer one should be weary of hiring a coach who claims they're an expert at all things fitness and health. No one coach is THE BEST at building muscle, losing weight, sports performance, rehabilitative exercise, and nutrition.
Lets take Mike Reinold of Champion Physical Therapy based in Boston, Mass who is an extremely talented Strength and Conditioning coach and PT (Physical Therapist). Does one think he is not capable of working with physique competitors? While he's most likely well versed in the process, his main business is working with athletes and post rehab patients. He wouldn't be setting himself or his client up for the best chance at succeeding.
On the other end of the spectrum lets take Bret Contreras who runs the Glute Lab based out of Phoenix, AZ. As a PhD researcher he's one of the leaders in glute hypertrophy (muscle building) and if someone came to him with a SLAP tear of the shoulder, Bret would have an idea of what to do but this type of client would be better suited to someone like Mike because that's his area of expertise.
Each coach is great at what they do and would most likely know what to do with their respective clients. If they however were able to swap people, they would have even better chances at success. Great coaches are well versed at all aspects of training but they know what one or two things they're actually "experts" in.
I am a former professional cook and Precision Nutrition level 1 coach, I feel confident in cooking healthy tasty meal prep for my clients. In addition to that, I am a well versed strength coach who uses strength to aide in weight loss and rehab.
I know how to put muscle on, as well as improving sport performance, but if I received a client whom I thought a colleague would better suited at aiding the client, they'd be on their way with a referral.
In my opinion, looking for a coach who can succinctly state what they're GREAT at is one of the things I would look for in a coach or personal trainer.
Jack of all trades, master of none