I wouldn't say that. They obviously have some knowledge if they're certified. I'd just check which certifications they have, if they're certified by the ACSM, I'd say go for it...that test is the real deal.
A personal trainer can help if you're a beginner, if you've been training for a while, you most likely have picked up on enough to keep growing.
A personal trainer can't hurt, so if you've got the money...go for it.