About 10 years ago some friends bought a 2500 Suburban. The deal was quoted with them trading in a 4 runner. They didn't like the trade-in amount, so they bought it straight out - here's where the sales department goofed. They had figured that trade-in ripoff into the price - and sold it for that amount. The salesmen called them a week later and said they goofed $3,000 in the buyer's favor, so would they please come down and pay the extra? The buyer asked them to provide him with the name of anybody they had called after a deal where they offered money back to the buyer because they goofed in the dealer's favor - that ended the conversation.
Unless this dealer is family or something, they shouldn't have called you.