The dealer is only interested the value of the transaction as a whole. There are two elements in this, the cash you give him, and what he considers your old car to be worth as an asset. Some dealers will give you more for your old car than its asset value, but compensate by giving you a minimal discount on the new one. Others will discount the new car heavily, but offer a lower figure for the trade in. It all depends upon which strategy they think is more likely to maximise the amount of cash you are prepared to hand over to close the deal. When they sell your old car, the same factors may come into play, so they could well be happy to sell it for a supposed sum that is less than they appear to have paid for it.