Once the dealership takes possession of the car and deals with your lending institution, the dealership gets the title. The car then becomes theirs to sell, whether to a retail buyer or -- more likely -- at a wholesale auction to another dealer. Don't Forget. Just because you're trading in your used car doesn't mean you no longer owe any money Knowing your car’s value can help you get a sense of what a dealer may offer for your trade-in and negotiate a trade-in price. How car depreciation affects your vehicle’s value 2. Determine whether you still owe money on your current car. You may be upside down, or have negative equity, on your car loan. Trade-In Process. Trading a new car, even if it is only a few weeks old, works just like trading a car you have had for years. When you trade your car at the dealership, the dealer will assess the car’s condition and determine a trade-in value for the vehicle.