Easy. How willing are the clients willing to pay? A happy client is a sign of successful therapy, and happy people will probably pay with little fuss. ;-) And if you didn't notice, the original post was highly facetious.
I'll admit, most therapists probably do good work. I went and saw a school psychologist once and only once. I never went back because the guy was nutso. But I have been on good terms with therapists and friends with some, though not good friends.
I met a speech therapist who took me aside as a kid and offered to help me with my lisp. Up till then I had no idea I had a lisp, and nobody had noticed one either. I now have a lisp, and nothing will get rid of it. It is barely noticeable though, and only comes out strong when I get dehydrated or tired of enunciating.