Insurance Companies will not insure a Personal Trainer unless they are Certified.
Maybe it's different in different places. When I first started coaching at my old gym, they did not require a certification. They did require trainer's insurance, which required me to create an LLC. The insurance I used did not require a certification.
Regarding
@Abishai 's reply (sorry you kind of got dogpiled on....):
-I have met many super strong athletes whose coaching abilities were mediocre at best. I have always been into calisthenics, and that corner of the fitness world is FULLLLLL of super strong people with terrible-to-mediocre advice. They are strong, lean, have big muscles, and can do cool feats, so people want to follow how they got there. Sometimes it works to follow suit, sometimes not. There are also some people in that community that use a lot of evidence-based approaches, and integrate principles from other strength training modalities.
Again, a good trainer needs to be able to prescribe exercises particular to a client. This was my personal struggle when I taught group calisthenics and handstand classes. The range of what each student needed could be pretty varied, so I had to find ways to make it work in a group setting. Personal training was easier because I could deduce exactly what each client needed for their particular goals and situation.
That said, I will repeat what I said earlier, as I believe it is an important factor:
-Most certifications
do not require hands on experience, which is the most important part of becoming a good trainer. Even the CSCS, which requires a bachelor's degree, does not (to my knowledge) disriminate what that degree was in. You could have a BA in economics and get your CSCS, never having worked with people. I would 100-times over prefer someone without certs, who produced the results I am after, than someone with alphabet soup after their name who didn't. I would especially prefer someone with less credentials who was pleasant to work with than someone who is not. I have seen trainers with credentials who were terrible communicators. I know that's a bit of a generalization; I am
not saying that people with certs don't produce results.
-regarding the "physique" portion: There are trainers, PTs, etc out there who do not have impressive physiques but produce great results in their clients. That said, they probably get overlooked by some people because they don't "look the part." If I am doing this as a side-gig, I feel like I ought to at least partially look the part, and partially look like I know what I am doing. This is especially important to me, if I am to attract clients outside of my social network.