How to find ture and fair value of a used car when buying private?

I was told KBB is not a reliable website to search for fair value. I have looked into Carmax and Autotraders and Edmunds and few other sites, but besides KBB I was unable to find any feature to calculate price of a car. Any ideas?|||kbb.com is actually pretty good...don't believe everything that you read. You could also call your insurance broker....they have the prices on-line...ask them if you have a specific car in mind|||Actually I would find the red book value,check the car over and try it out n the road.