Best Buy has never been as strong as Circuit City in car install business. some points I heard like no custom items if it doesn't blot in we don't install it is correct. Its not on the installers, its just the company in general. we can make amp racks and little stuff but not boxes simply b/c we sell a lot of custom boxes for vehicle online and can order them thru a manufacturer.
As far as musical instruments part is wrong. they're are not replacing 12 volt with guitars n stuff. They just invested a lot of money into 12 volt bia products, but your right staffing on the sales floor runs as a flex type dept. different areas in the store converge that dept if there are no installers on the floor. At least in the smaller stores. the bigger ones do have dedicated sales staff but those stores are like Citrus Park, Clearwater, S. Tampa, and i think Brandon but not sure.
I think the person makes the installer not the company. I'm sure some of you brick and mortor stores can attest to going thru 5 crappy installers to find 1 decent installer and sometimes you get lucky on the first shot. I work at the Spring Hill Best Buy (which is a smaller store)as and installer so i can only give definitive info that location. but hopefully that answers some questions you may have had about Best Buy.

btw yes we are selling Kicker right now and will have a best buy only Polk Audio line of speakers (which i think are restamped DB series) and their regular amps in July.