Say I went to some computer store, so that i can have the put together the specific parts i wanted, but he gets those parts himself. Will the quality of those parts differ when compared to the same exact parts bought on newegg.com, tigerdirect, etc?
That depends, you will always want to go with brand name parts.. the best thing to do, Is Research...And shop around,NEVER GO WITH THE FIRST PRICE...
The research is for you to do. The salesman can tell you the parts are from MSI, ASUS... whatever. It's up to you to look at the brands he uses when he puts the parts together. Any chance you can give us a list of parts you want to put together? Let us know what he's charging you so we can distinguish between the price of the parts and his premium.
What i mean is, if i am looking to buy the i5 2500k processor, or the EVGA GeForce GTX 580 (Fermi) 015-P3-1580-AR Video Card, will all versions of these specific parts be the same, no matter what website or store i buy from?
Yep. A possible difference may be that your retailer may use a Retailed item and install the hardware without giving you the full contents of the box. For example, some Retail video cards come with extra wires or free games. Your retailer might choose to withhold those items for himself. To make sure, just ask him if any games, cables, or any cool extras are included with the rig!