quack; fake doctor
A person who practices medicine without a license or proper qualifications; often used in news or warnings about medical fraud.
The fake doctor was arrested.
It's dangerous to be treated by a quack.
ヤブ医者 is a colloquial term for an incompetent but licensed doctor, whereas 偽医者 is an unlicensed fraud.
Standard kanji spelling.
Mixed kana-kanji spelling; less common but still used.
Compound of 偽 (にせ, 'fake') and 医者 (いしゃ, 'doctor').