I worked at Best Buy last summer, but it was only to add something to my resume, keep me busy and out of trouble (j/k on the latter), and totally rape the Home Theater department with my discount on the last day (my Dad thinks I pretty much gave all their money back to them). The mark-up depends on what department it is.
Car Audio= MASSIVE markup.
Home Audio= MASSIVE markup.
Computers= Little Markup.
Media= Very Little Markup.
Appliances= Can't Remember.
Video= Large Markup.
Accessories= Crazy Hella Insane Markup!!!
I'm too tired to do the math, but here's some things I got at my price vs. consumer price (these are June-August 2001 prices)
Sony Xplod CD deck: Me= $134. You= $199.
Toshiba 27" TV: Me= $252. You= $299.
Sony 12" home theater subwoofer: $112. You= $199.
Sony 500w x 5 home theater reciever: Me= $212. You= $299.
Sony 5-disc carosel CD player: Me= $83. You= $99.
Cell phone belt swivel clip: Me= $1. You= $9.
Acoustic Research optical coaxial cables: Me= $3. You= $19.
Monster Cable Interconnect cables (nice stereo RCA plugs): Me= $6. You= $12.
Monster Cable 100' spool of speaker wire: Me= $31. You= $60.
I also got Performance Service Plans (PSP) on nearly everything I bought there with my discount- never paid more than 6 bucks for a 4-year plan (like on the TV). Working there sucked. The discount rocked.