No one blames you for seeing a well-muscled personal trainer at your gym and thinking, “What could that kid possibly teach me about fitness?” Just 30 years ago the field of personal training was highly unregulated. Anyone who’d spent a couple months in a gym could hang up a plaque and call themselves an expert.

But today’s personal-training industry is not what it used to be, with trainers typically boasting multiple certifications, and in some cases, degrees. So yes, they can teach you a thing or two about fitness, and you should listen. But if you’re still convinced you know it all, check out this list for the tell-tale signs it’s time to invest in a trainer of your own.