First Time Maserati Buyer

I have been waiting for the right time to buy a Quattroporte and the time is very close I just need to find the right one that is fairly close to where I live. For those who have owned QP's in the past and for those who know much more than I, I ask for your assistance.

I have found my favorite color combo but buying one from a private seller has me slightly worried.
here is a link to the car Maserati Quattroporte | ksl.com

It's a 2006 Sport GT it looks like it is in wonderful condition and the seller claims to have the last major done 8K miles ago with a new clutch.

I am trying to get a good pricing guide on this car NADA has it as high as 60K and KBB has it as low as 43K, I know the two are never the same on any car but that is a huge difference. Is there a way to judge appropriate value for a car like this?

Any suggestions would be great, if anyone has the ability to seek the cars history it would be more than appreciated.