I have a somewhat similar story, though it happened after the car was purchased, papers signed, and the car was brought home. The dealer called because the bank didn't give us the interest rate we had agreed to. The difference amounted to something like $420 total - so, $7 more a month. I said "no", and since I knew we'd have to sign new papers for this to happen, I told them I'd just drop the car off the next morning and that they could keep it. They were astonished, and to be fair, I don't think they were scamming me. But when I decide on a monthly payment, I never budge..not even a dollar. They found another way to make up the difference and we kept the car at the same price.