I had a similar experience with Carmax. I recently sold a 2009 Traverse. Carmax was my first stop. They were 4k under KBB trade in on a loaded low milage well maintained car. Next place I took it offered 4.5k more with only a 15 minute review time. So I shopped it around to several other wholesale buyers and eventually sold it for $4990 above Carslacks original offer.

Imo their set up allows for a low ball offer on every car because if they don't buy yours there are 30 more waiting in line for evaluation. I sold mine to a small dealer who gave me a fair price and who sold the car in two days again at a fair price.

I am with Woody, Carmax is a rip off at least if you are on the selling end.