It happens everywhere.
I left a hair dressers many years ago because they put their prices up massively and we're still paying the hairdresser minimum wage.
This is why most PTs at self employed. They pay rent to the gym and keep the rest.
Most people applying for this job will only just be qualified and looking for experience. Which is why lots of employed PTs are not the best.
They are PT/fitness instructors and sales people.
However they do get paid for free sessions, because they are on a wage.
Where self employed PTs who offer a free starter session are doing it for free.