One of the big problems you often see when purchasing from a non-authorized dealer, is they'll strip the extras that Apple bundles with the machine, and sell those separately.
There's a place near me that does that; Go to buy a replacement power-supply and they will have taken out the cord and wall-outlet adapter, and put those in separate bags, forcing people to buy them separately.
Apple's prices are reasonable, as are the prices from Best-Buy or other authorized dealers, and to avoid any BS like those other places I stick with the real-deal.