Like a college degree, or a black belt in the martial arts, having a "trainer certification" doesn't mean you know anything, or are going to be a "success in life", or can actually defend yourself!
All of us "vets" in the iron game have seen in the gym during our workouts, time after time, where some PT was putting one of their clients through a workout and we had to literally "bite our lips" to keep from going over there and saying to the PT (words to the effect) "where did you pick up that hair-brained exercise". or..."where did you say you got your certification"...??!
I imagine it means a little something to have a certification after your name and it may help land a first job...but you have got to have the training knowledge gathered through a constantly evolving study of training methods, the salesmanship, and the people skills, to be a successful PT!
And, I might sadly add...nowdays...you have to practically have the pharmaceutical knowledge of pharmacologist to satisfy some of your clients/potential-clients needs!