I have a dentist, and a doctor who have pissed me off for one reason or another, and in each case after thinking about the situation I called and explained my problem, feelings etc about that situation. Whether it was about treatment, or the cost of a procedure. In the case of a dentist I was made to feel understood, and appreciated. In the case of the doctor who was not born in this country, and did not share my feelings and basically told me i was wrong, I posted my feelings, evidence and named names, and found another doctor. That doctor has since left this area, for a more metropolitan environment where he does not have to deal with us local yokels.
In each case I had signed such an agreement without realizing what I was signing, and in each case I did not care. I posted my feelings evidence according the rules of the internet posting service, and gave my real name etc so people who came across the reviews would have more confidence that the review was genuine and not some paid for result.