I worked at Sam Ash for summers during college. There was a Guitar Center right next door, so you can imagine how that went for haggling and price matching. At that time (almost two years ago) they definitely paid on commission at GC, as I had friends that worked there, but it's possible things have changed. They definitely still pay commission at Sam Ash.
The margin on the big name items isn't as high as you might think. Every sales rep has the authority to knock of tax, but it KILLS the commission rate. Any significant discount beyond that and it isn't worth the trouble to sell. But, in a crappy economy, you have to take every penny you can get, even if you feel like a hobo peddling garbage on a corner because the customer insists on saving $7 on a $200 guitar. The customer doesn't know (or just doesn't care) that that $7 means a lot more to the struggling salesperson who is trying to break his weekly base sales than it does to the customer.
Profit margins in retail are very low. I hate when people feel like stores OWE them a huge discount just because they've bought something in the past. It's business, and the salespeople don't make jack. You're not a "valuable customer" if you go in and bust everyone's balls to give you something at purchase price. You're just an arrogant consumer trying to nickel and dime at other people's expense. You're not "sticking it to the man," you're just making it harder for the workers to get by. And these are guys that are making a crap of a lot less money than you.
I fully understand not being able to afford something you want. Fortunately, with the internet, it's easier to buy used than ever. The prices on used stuff are better than you can screw Sam Ash/GC over for anyway. If you insist on haggling for a deal, do it on the used market. This widespread ball-kicking of the retailers and the manufacturer's is NOT good for the industry, it's making everyone poorer. If this trend continues, it will lead to them NOT being able to provide the gear in the first place. If you don't believe me, do a TB search for LOUD TECHNOLOGIES.
Anyway, this rant was not directed at you personally, xbrandonx.