I'd say that is DEFINITELY going to differ from location to location. I'm sure there are some very fine installers working in some Best Buys and some very crappy installers as well. It's a crap shoot unless you can get some references from prior jobs. Hang out outside the install bay one afternoon ?
And of course the exact same could be said about any and every install shop.
I had a system done at Best Buy, and they did a very fine job. He installed the amp inside wall panel in the back, and he rain the remote gain knob for my subwoofer to a spot inside a cubby hole in my dash to make it easily accessible AND invisible. You would
never know that there is a custom system in my car just by looking. I kept the factory head unit because a pretty decent one comes in the Scion tC and I didn't want to pay a bunch of money to keep my steering wheel controls and my remote MP3 jack.
I
have been having a few issues with the unusually cold winter weather and my amp not kicking on until it warms up. I think this may be because the way the amp is mounted it actually contacts the external sheet metal/frame of the vehicle so it is fully exposed to the cold. The system was installed in December of '06 as soon as I got the car, and it's the first time I've had temperature issues due to the installation. Honestly I would have had much more concern about the hundred degree heat in the summers. As long as the issues never get worse (the cold
has been an extremely unusual for the area) I'd say it's a pretty decent trade off for the complete invisibility of the system.