I suspect the low tread reading the fitter just happened to have put the depth gauge on the raised low tread marker.

Notice how we've lost 1mm off tyres recently, they were nearly always 8mm (or more for all terrain tyres) but now many are 7mm to start with.

Edited by gordonbennet on 30/05/2018 at 18:32

Why not buy a tread depth gauge and check them yourself, not expensive. I would suggest that the person who checked yours was either blind or mad, possibly both......

.......and sadly the true rip-off here is that you were probably being charged around £100 per hour for his diligent incompetence. I trust the door hinges were lubricated. Check the oil level (assuming replaced) is not above the max mark.