Most customers don't. Dealers provide information that is biased toward specific models or option configurations that they happen to have on the lot. Customers expend a lot of physical energy trying to correct these asymmetries, pitting one dealer against another. They then expend emotional energy on haggling. The deconstruction of the supply chain.
Today there is a shock wave called the Internet.
I think we recognize that it's there. The Interent is not going to get rid of the dealer. I know there are advocates such as J.D. Power who think there's some sort of different distribution system about to emerge, but that's not going to happen. In a world where everyone and everything is connected, the shortest distance between a customer and a firm is one mouse click. If the pundits are to be believed, middlemen would become the roadkill on the information superhighway.