It is just the old trick of a cheap offer to get you through the door by the look of it. Changed front pads on a 3 year old 20,000 mile Corsa which had not long had it's 'main dealer' service and happen to say 'did they look at the rear brakes?' I don't think the drums had ever been removed since it was built and the customer was most surprised! Still they won't be going back to the main stealers now!