You'd be surprised how many shops are out there that don't actually know how to use their machines properly. I would recommend you look for a shop who use a Hunter GSP-9700 road force balancing machine. The Hunter GSP-9700 load roller applies a force of up to 1400 pounds against the rotating tire/wheel assembly as it performs the Road Force Measurement. Basically, it simulates the wheel/pressure as if you were actually driving on the road for the most actuate measurement. You can located the nearest Hunter GSP-9700 near you
here.