When it comes to ASSuming someone knows better, you can never let your guard down. I didn't trust the local Big Tire specialist's to remove or replace my wheels when I replaced my OE run-flats. I ordered a stock size set of Michelin PS4S's and took them in the wife's Subaru with my Camaro's wheels/tires to the tire shop for mounting and balancing.
When I got home and started to put them back on the car, I realized they had put the back tires (275mm) on the 8.5" front rims and the 245's on the 9.5" back wheels.
Just cuz yur paranoid doesn't mean they all aren't out to get you!