To be both quackery and fraud, the quack must know they are misrepresenting the benefits and risks of the medical services offered (instead of, for example, promoting an ineffective product they honestly believe is effective).
In addition to the ethical problems of promising benefits that can not reasonably be expected to occur, quackery also includes the risk that patients may choose to forego treatments that are more likely to help them, in favor of ineffective treatments given by the "quack".
The few effective remedies sold by quacks included emetics, laxatives and diuretics.
Quackery is often described as "health fraud" with the salient characteristic of aggressive promotion.
Since it is difficult to distinguish between those who knowingly promote unproven medical therapies and those who are mistaken as to their effectiveness, U. courts have ruled in defamation cases that accusing someone of quackery or calling a practitioner a quack is not equivalent to accusing that person of committing medical fraud.
Grandiose claims were made for what could be humble materials indeed: for example, in the mid-19th century revalenta arabica was advertised as having extraordinary restorative virtues as an empirical diet for invalids; despite its impressive name and many glowing testimonials it was in truth only ordinary lentil flour, sold to the gullible at many times the true cost.
Even where no fraud was intended, quack remedies often contained no effective ingredients whatsoever.
A quack is a "fraudulent or ignorant pretender to medical skill" or "a person who pretends, professionally or publicly, to have skill, knowledge, or qualifications he or she does not possess; a charlatan or snake oil salesman".Common elements of general quackery include questionable diagnoses using questionable diagnostic tests, as well as alternative or refuted treatments, especially for serious diseases such as cancer.