Norfolk Trading Standards Service inspected two second-hand car sales premises on Tuesday, October 6.
Five vehicles were checked for roadworthiness and one was found to be unsuitable for the road.
Investigations into the vehicle are now ongoing.
The discovery has prompted a warning for drivers to carry out checks before buying a used vehicle.
A spokesman for Norfolk Trading Standards Service said: “Second-hand car sales are one of the sectors we receive the most complaints about, so we would encourage buyers to use our handy Car Buying Checklist to help make sure they get what they pay for.
“Drivers can also check a vehicle’s MOT history on the GOV.UK website to compare the advertised mileage with records from previous MOT tests.
“Anyone who believes they have been targeted by a rogue trader should report it through the Citizens Advice consumer helpline.”
The service also reminded second-hand car dealers to follow guidance on trading legally and responsibly.