There are bounds of reason. My dad's old gym had this trainer there who was about 5'5" and looked like a doughnut lol. About as wide as he is tall (not in a good way), and always wore compression shirts. So that guy is probably not a good example of "practice what you preach."
But if someone is in decent shape, maybe doesn't have a 6 pack or anything, but has some muscle on them, fairly lean, lives a healthy lifestyle, then I don't see the problem with that. Not everyone can look like a bodybuilder, or even want to look like one. I find with my physique I attract more office workers and people who just want to get in decent shape for the summer. I'm not a big guy, I'm not ripped year round, but I look like I lift and keep a decent diet year round.
I have a good friend who is a powerlifter, and when I first met him I honestly wouldn't have been able to tell he works out at all lol. Would've thought he was just a fat guy. But then I saw him bench 500lbs and shut my mouth hahahah. So maybe he doesn't LOOK like what the majority want to look like, but that doesn't make him a bad trainer. He's gotten plenty of people in shape for bodybuilding, mens physique, bikini, figure, etc... even though he doesn't resemble that demographic.