My guess would be they will haggle if the buyer wants to haggle. They aren't going to give up a sale. But, I've never shopped CarMax so I don't really know.
I had a roommate years ago that worked as a salesman at CarMax. He had about the authority to haggle as the kid taking your order at McDonalds. I think the volume is so high that if you don't want it at the marked price, someone tomorrow will. Of course, that was years ago at one lot. YMMV.
