Medical quackery is a form of healthcare fraud that sells false hope. It preys on people suffering from diseases that may not be amenable to cure. Quacks promote unsubstantiated interventions that lack a scientifically plausible rationale. A quack may, however, be scientific in some aspects.
They may even front products and procedures that can be useful for some purposes, but worthless in other respects. You need to be wary of quacks, their drive has more to do with profits than your health.