Why does fraud exist?

The question can be seperated into two parts:
from the quacker's point of view or from the victim's point of view.

The quacker does it because there's a lot of money to be made.

And there will be victims because people want to believe there's something that can cure them.

Dr. Barrett gives an explanation to why:

Nearly everyone is vulnerable to one form or quackery or another. Five human characteristics contribute to vulnerability:

1. Lack of suspicion
2. Belief in magic
3. Overconfidence
4. Desperation
5. Alienation

I think Dr. Barrett might be right about this. I also think it's because most people let their feelings control themselves instead of using their brains. If you don't want to be fooled by health frauds you'll have to be more suspicious, realistic and skeptic about life in generel.