I admit to using part-worn tyres up to a few years ago as we don't do a high annual mileage, but went back to medium priced new rubber following what could have been a big problem if the PW had let go at speed. There is supposed to be legislation regarding the sale of part-worn tyres but I think there are a awful lot of cowboy outlets out there, most of them staffed by hairy-arsed fitters that just shove the trolley jack anywhere under the car & have never heard of wheel nut torque settings, so tough s..t if you need to change your own wheel.