They will just deny it and you can tell them till you are blue in the face and they will just say prove it......
My mate recently rebuit Torana dropped a valve while his mum was driving it, after that we checked the tyres and sure enough less tread........
The managers at these places don't give a fuk unless it is the product which was installed at their workshop, I will always wait now depending on the workshop or sit around the corner, cos really there is no reason they should have to drive the vehicle when putting on new tyres, thats why they balance them off the car,
Do you know how many K's they put on it? You might be able to use that to your advantage........

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RIP POSSUM
3" Invidia Zorst