Used Cars: KBB Value, negotiation tips, rule of thumb

Question
While dealing with private party, which of the value - Excellent, Good or Fair shall be used to negotiate? Any negotiation tips with private parties :) ? Thanks!

Answer
The condition value depends on... the condition... obviously... i consider an almost new (under 20,000 miles... under a year old) car excellent... anything that is not completely showroom but still in good shape would be a Good condition... Fair would be with some known mechanical problems or body damage... I usually use the Good setting as a rule of thumb, unless the car is damaged or poorly running.  As for negotiating... research.. research... research, know the value of the car in question, know how to look for damage/problems... ask to have a mechanic check it out.. take some one who knows cars with you... if you know the value (or even have a printed out blue book or NADA value) - that can help.. Private parties are less flexible than dealers, so expect them to only come down about 1000 from the price max.. start by offering ~1000-500 under what you think its worth, then negotiate up to a fair price you both are happy with.  If they want to much, dont be afraid to say no thanks and leave.  thats about all you can do.