The Automobile Association and the Motor Trade Association say a push for higher standards among warrant-of-fitness outlets has been effective.
Thirty-five such outlets have lost their certification in the past five years, the associations say, because they were unwilling or unable to improve to the required standards.
Fourteen were struck off in 2008 alone - that was when the Transport Agency began its mystery shopper programme to test competency.
Five outlets lost certification last year and just one so far this year.
The AA's technical services general manager, Stella Stocks, says standards are improving.
