Failed MOT when should have passed, why???

Failed MOT when should have passed, why???

Took my 6 series for its first MOT to this dealer, they failed it on a small cut to tyre and obviously suggested I paid many 100s of pounds for a new one. The cut was very small (15mm) and no cords were showing, so next day took it to another dealer and showed them the cut and explained that Wollaston had failed it because of the cut, however, they said the tyre was legal as cut was less than 25mm so passed it with no issues. So why did Wollaston BMW fail it, to make a sale on a very expensive new tyre, or through incompetence? No idea, but wouldn't surprise me if the MOT guys are on some sort of 'unofficial' bonus! My advice, don't risk your hard earnt cash, take your car to an independent garage.