There are a couple of resources when trying to determine a car‘s fair market value. The most commonly used pricing resource is Kelley Blue Book. KBB is easy to use and provides fairly accurate prices. It is important to be realistic when assigning your cars condition. Another resource for used car pricing is NADA. The National Automotive Dealers Association site provides pricing guides for used vehicles. Their guides are often used by car dealers to help assign values to trade-ins. The best method is to check both guides and set the price for your vehicle slightly below the top end for the condition.
For more info, see How the Actual Cash Value is Calculated