Yea the KBB on the Audi 2.7T I bought was ~$16900 and I got the car for $14500 (that included negotiating as well) so you are right its never correct. Honestly, we have the 4.2 Q7 and when it was in for service we got the 3.6 which didn't feel as good to drive as it had less raw power and also didn't sound as nice :)

I am not a good person to ask on price. I have only bought new cars and then traded them in at the dealer where I have always received KBB's number plus a few hundred for a trade in. Based on my trade-in experience, and KBB's trade in value for my car, I would expect to receive about $26K for my car. So the $23K you have seen seems to be a pretty good price. However, according to Audi's response to my inquiry of a few years ago my 05 4.2 is one of only 83 truly fully optioned 4.2s brought to the states in 05, so my car is better optioned than most.

Make sure you get a copy of the service records and I can't stress enough that you verify that the MMI has been updated. The updated MMI makes a huge difference in this car.

Good luck.

no price sounds good without CPO next to it