Past experience with CarMax was positive but recent experience with CarMax in Laurel, MD, suggests the franchise has gone downhill. It's capitalism, yes--they make an offer, I accept or reject.
But when CarMax offers more than 40% lower than a dealer (outright offer, unconnected to new-car purchase) and more than a third lower than all the standard appraising sites (KBB, Edmunds, black book, etc.), I become suspicious. Does CarMax really expect to get away with offering nearly $5000 less than the dealer and $10,000 less than identical vehicles currently on their lots? The vehicle in question was "like new" and reconditioning it for resale would have required little if anything--I'd just had it washed and waxed and the oil changed.
Anyway, buyer (or in this case, seller) beware. Take your vehicle to a couple of dealers (same brand) and if you have a vehicle in good shape, you will probably do better than taking it to Car Max.
Product or Service Mentioned: Carmax Oil Change.