Partially, because I have had my moments at Best Buy. Like when they advertised a CD-R as "minimum 5 per store, no rainchecks" and I got there 5 minutes after the store opened and... no drives. Ah, but I tricked them... how many did you have when you opened today? Two. Ah, but your ad says etc and this is a misleading advertisement. I should report this to the BBB etc etc left the store with a comparable drive for a similar bargain.
More recent incident was a "12 months no interest financing on all computers." Ah, but this is Best Buy land. Laptops aren't Computers and therefore didn't qualify for the offer. Oh, what they meant was computer packages, and notebooks aren't packages. Fortunately, I had other methods lined up for the laptop.
So, I'll agree with the Best Buy Sux people, yeah, they can be stupid at times. But... taking your non-functioning computer in to a bunch of minimum wage monkeys expecting they WANT to fix it? Uh, yeah, sure. Each computer I've bought at Best Buy had a manufacturer's warranty and I've worked directly with them. My desktop included one year of in-home repair service. It was an early 1GHz Athlon, and, yes, the processor died once. Two days for parts, and the following day they sent someone here to do the swap for me. No problems since then.
Just... don't expect the people to know more than you do. You're buying, you have incentive to lean and be informed. They get minimum wage. They just want to make their managers happy so they might get paid more, and that means selling all the junk you don't want.