Adelaide police have visited used car yards to crack down on any dealers selling unroadworthy vehicles.
They say 28 used cars were defected in an inspection of 68 vehicles across three dealerships in Adelaide's north-western suburbs on Tuesday.
Acting Senior Sergeant Geoff Rodda said one car was found with severe oil leaks, faulty brakes and dangerous electrical wiring.
He said dealers who were blatantly breaching the law were putting car buyers in danger.
"They need to be honest and reliable in their dealings and, if they're not, if they're trying to sell defective cars we'll be coming back and we'll be getting there and we'll defect your (sic) cars and they won't be able to sell them," he said.