BOY THATS A STUPID QUESTION.
Because if you use it and still look like shit you will complain that he recommended it, and he gets in shit.
BOY THAT'S A STUPID ANSWER
I'm a gym owner and have been a trainer for almost 15 years of pro athletes (nba, nfl, mlb), olympic hopefulls in figure skating, martial arts, college baseball, football, etc etc and 3 ugly lesbians to boot. Here's my 2 cents.
If he trains you and you look like shit, it doesn't come back on him according to your logic? The reason is because of liability.
Most big gym trainers aren't allowed to give nutrition advice beyond the basics because most aren't qualified. NASM and ACE certs aren't where you're going to learn anything beyond formulaic training principles that focus on core stability, etc.
To address the original poster, the fact that this trainer in the gym is big and looks good is neither here nor there. People seem to assume that the big guy is the knowledgeable guy. The fact is he may be the genetic guy and/or the drug guy. Maybe too, he is the guy who'd know. The point is, you can't assume his level of education based upon his physique.