If you have an old car that you are considering trading in to purchase a new one, it is often better financially if you sell the car yourself, especially if the car is in excellent condition with low mileage. However, if your car has mechanical problems or is in poor condition, it may be difficult to sell. In that case, it is better to trade in your current vehicle
at the dealer to lower your down payment when financing.
Keep in mind that no matter what condition the vehicle is in, the dealer will offer less than the trade-in value. You will need to factor that in when determining how much you will have for a down payment if part of that down payment is the trade-in.