People can volunteer for studies: Clinicaltrials.gov in the US lists studies from all over the world. Type in PTSD and the randomized controlled trials, observational trials, etc are listed and described. No one has to pay a fee for participating in funded studies - in fact you frequently get reimbursed as well as meals, lodging, and medical tests required to participate.
The people who decide if studies whould be funded (the reviwers) are both government and independent experts. My psychiatrist is an independent reviewer who is board certified in neurology and psychiatry. He takes his review work very seriously and looks at the science behind the proposed studies. He also suggests other scientists' studies for his patients if he thinks they will benefit.
Anyone who would charge you for an unproven therapy but call it science, proven-by-testimony, isn't being ethical. If they tell you it is experimental and you want to pay the fee to see how it goes, then you give your informed consent.
The people who decide if studies whould be funded (the reviwers) are both government and independent experts. My psychiatrist is an independent reviewer who is board certified in neurology and psychiatry. He takes his review work very seriously and looks at the science behind the proposed studies. He also suggests other scientists' studies for his patients if he thinks they will benefit.
Anyone who would charge you for an unproven therapy but call it science, proven-by-testimony, isn't being ethical. If they tell you it is experimental and you want to pay the fee to see how it goes, then you give your informed consent.