I had a very similar experience in the field to what Batista had. Here were my reasons for doing a PT course:
1) I (thought) I knew that I definitely didn't want a desk/laboratory job.
2) I knew I didn't want to study for 4 years before starting earning.
3) I knew that I was great at sports, fitness and the sciences.
4) Having a passion for sports and fitness, I figured that PT was a great fit for me.
5) The idea of a self influenced earning potential appealed to me. Who doesn't like getting paid much more money for the extra hard work you put in.
In reality though. My experience was similar to Batistas in many ways.
I am not a big buff guy, never have been. I was always the athletic type, 1st team and provincial in multiple sports etc. but not being buff immediately cuts out 50% of your client base. The big okes at gym don't want to take PT advice from someone with smaller arms than them. So you have to decide to spend all of your free time on buffing yourself up massively. If that is not the type of body you want to have, say goodbye to 50% of your potential clients.
Of the clients that you do get, most will flake out on you, never completing their pre-bought sessions. But always scheduling them. So you waste your time and money going to the gym to meet them.
Of the ones that do pitch up, most will drain the will to live from you. 95% of clients do not want you for your knowledge, they want you to be the strict old parent that forces the bad vegetables down their throat at dinner time. You spend your days, convincing the same people, of the same good sense of exercise and healthy living that they heard two days ago. Half the time you have to badger them with the convincing on the phone.
Your job starts to become far less about your knowledge as a fitness professional, and far more about the Kindergarten teacher™. It is spirit draining to say the least.
This is where I am going to tell it like it is and be a little contradictory, but here goes.
Your son, indicating that he wants to do Pilates instruction, will not be a buff dude I imagine. So his only hope is massive amounts of charm and charisma combined with being EXTREMELY good looking. The facts are that if he isn't getting the big buff guys, his client base will be made up of bored housewives and rich varsity girls. These women choose their personal trainers based on eye candy and feel good motivations. They want a PT to have a really ripped body and natural good looks, be very charming and in many cases flirtatious, to make them feel good about all the training they are doing to reachieve/achieve that sexy body.
If your son manages to fit the criteria for breaking into this particular market. It is a very fine line to tread, on being flirtatious and suggestive, without actually going any further.
That is not all the women of course. Many are just hard workers that enjoy your training methods and appreciate your knowledge and company during their training session.
But the facts are that the two largest groups of consistent clients are short sighted big buff guys that wont take advice from someone much smaller than them. And rich women that want to feel good and get trained by someone who makes them feel that way. These are the clients that will keep coming back to you if you give them what they are after.
The rest of the people are non-repeating turnover. They come to you because their doctor/loved one gave them a reality check bitchslap about obesity and heart disease and not seeing their grandkids grow up. They hardly ever keep the drive to come back week after week, regardless of all the effort you pour into keeping them motivated.