Should you look at their academic qualifications, number of courses attended, degrees achieved, Personal Training Certifications and number of years in the industry? Should you look at how they looK - If they have the type of body you want they must be good, right? Or, should you go with 'word of mouth' ans see who is the most popular or the most expensive, they must be good right?
If you do, then you are searching by the personal trainer that has the best marketing skills.
I can't answer this for you but I can give a some examples of why our best lifters who achieved world all-time rankings lifted.
Powerlifting has changed from the authentic old school lifters to the new internet hero worshipping wannabe's. There is a whole group of authentic old school lifters, who are not on the internet and want nothing to do with the people on it. They got burned ealy in the first powerlifting forums that gave voices to wannabe's who became internet experts and began lifting themselves up by keyboard bashing our best powerlifters.
Let's go back a bit when authentic became something the wannabe's wanted without paying the price. When I was in school a new pair of jeans was something to be proud of. They were new