Any seller should expect you to turn the car around before making a decision, so use this time wisely. Testing a car is not just about checking if it feels good. Be sure to check according to our 14 things.
Diesel engines are generally more fuel efficient than gasoline engines. But don't be fooled to think that this will definitely make the diesel engine a better choice.
If you need to whip your current wheel, you have two options. You can partially replace the car at the dealership, and the dealer will give you a price and then deduct it from the total cost of the car you purchased. Or you can sell it privately - there you list the car and get cash from the person who bought the car.