He probably thought you knew what you wanted which has always been the case with the majority of people who walk through the doors because they are geeks.
Did you bother to ask his advice?
This is why the last time in actually went into a PC parts store (not OC but I'd say equally as knowledgeable) I walked in with my list and spoken to the lass on the desk. Explained that this was the list I'd come up with and my total budget. She changed about 4-5 components, even adding discounts where she could and I walked out with a much better system and a greatly inflated opinion of the company.
Though this was back in 2008.