In DC, the dealer I bought my '68 from would take in cars and load the up with dealer add ons. The higher profit was in the extras. They would put the extra stuff on the car before it hit the sales lot. More popular models got more add-ons even though customers didn't want them. Less desired models were left alone. If you wanted a deep discount, you bought a factory economy version that they left alone. That tended to be the 350/3spd column shift. The 400's got dealer options tacked on to run the profit up. Popular features here were door edge molding and chrome door edge guards. Nothing left the lot without "gas, glaze and undercoat" charges.