a person who falsely claims to have special knowledge or abilities
charlatan - fraud
A ‘charlatan’ is somebody who seeks to deceive others with false claims in order to further their own interests. Such people typically appear in complex fields that the average person may not have the technical expertise to fully understand, such as healthcare and finance.
I hired Peter because he convinced me of his abilities, but he turned out to be nothing more than a charlatan.
Some claim to have been helped by the faith healer, but others believe that he is a charlatan.
People advising get-rich-quick schemes are usually total charlatans. Stay well clear.