What is an example of quackery and self-fulfilling phophecy?

Suggestibility. If you are told that if you pray long and hard good things will come your way. Soko gokai.
A familiar ploy. You come to an unscientific practitioner complaining of shoulder pain. You get a bogus exam, a learned and concerned and caring look, and then you hear -- "has the other shoulder started hurting yet?".