For example, if you buy a new car for $25,000 and trade-in your old car for and so many other hazards, selling your car yourself can be potentially dangerous. Autotrader provides advice on car values and tips, so you can get the most for your car trade-in and make the trading process easier. You can also get a Kelley Blue Book (SM) Instant Cash Offer and use it toward the purchase of another vehicle, or walk away with cash today. If you own your car outright, the dealership will apply your trade-in amount to your new vehicle. For example, if you purchase a car for $25,000 and the dealership gives you $6,000 for your trade-in, you only need a loan for $19,000.