I am in need of new tires. I caught a brass nail in the front last week and the back had over 7000 miles put on it last year. All of the local shops around here claim that I can't buy tires first and bring them in to be installed because its a "liability." I would think if I brought in my own tires I would save a little money (lowest quoted price for a pair of pilot powers + installation was $339) I've never bought tires before so I dont know if this is a normal thing or not. Any insight?