A lot of the Boxster out there are below KBB value nevermind the NADA value which is usually much higher. Is it a private party of a dealer? If it's a dealer then it is priced $2,135 below blue book. You can try and knock of atleast a grand if you haven't started negotiating yet. The car is only worth what it's worth. The book value is just a guide. If's it's a big dealership they have to make atleast between $2k-$5k or maybe more. If it's a used car it is unlikely that you'll find out how much the dealer paid for it. Here is a strategy:
Think about a reasonable offer. Get your finaces together and get your offer on paper. Go to the dealship and present the bank draft, if they take it, you got urself a good deal. If not, just let them make a counter offer and so forth. A good website too look at for that sort of thing is
http://www.carbuyingtips.com/used.htm
Hope this helps.
Alienz