I'm curious if there is an English word or idiom specific for a car mechanic that rips you off. In the case of a doctor, one could use charlatan, or quack.
Bodger — ODO
UK informal A person who makes or repairs something badly or clumsily.
Cowboy — Cambridge
UK informal A dishonest or careless person in business, especially an unqualified one.
"cowboy coach firms are alleged to have flouted safety rules"
An example can be seen on The Guardian "Round up cowboy mechanics, demands consumer body"
: not deserving to be taken seriously : having little value or importance
Substandard, poorly executed or organized. Amateurish.
Who's in charge of this mickey mouse operation, anyway?
Elkhart Lake — A racing school is a fantasy land business that leaves no room for Mickey Mouse mechanics or Goofy actions.
: given to making a quick profit usually by shady or irresponsible acts