first of all, there is diff value for different companies.
banks, finance comp and insurance company ususally use NADA.
KBB.com will give u a good range such as trade in or private party.
there is NO RIGHT figure. Just ball park figure and no, it is not a science to apraise cars. it is up to you to determine it.
Factor in what parts u r going to change down the road in 3-6 months. minus that from ur asking price.
what is the condition of the car? are they a dealer or private seller.
cars from dealers are usually cleaner and waxed, etc to make the sale easier.
private party, usually cheaper and car can be dirtier than cars from dealers.
ask for $6800 and see.
check
www.carfax.com also