No matter; I usually pay less than half buying parts (which are usually sold in a rational manner) and assembling myself.
But then again, the salesguy might be there to ensure future business. The next time you need a server, are you going to pick on the phone and give Mick a call, or are you going to waste your (presumably) valuable time doing some comparison shopping?
Maybe it's worth it to give the through-salespeople orders a discount because there's a person to person relationship built that encourages future sales.
In fact, I'm working on this subsystem right now. For large catalogs and large numbers of customers, this becomes quite challenging. There's a huge volume of data, and keep it current while product pricing, availability, licensing terms, etc. change, is tough.