Carmax has awesome prices on their new product. The same can't be said on thier used inventory. If you are looking to buy used I would recommend Enterprise Car Sales where they guarantee their prices are below KBB and NADA book. The also like Carmax have very ethical financing standards they have to abide by.
Carmax has great financing options where their lenders will often give high risk borrowers a better APR than most dealerships. The reason is that Carmax will buy back the car from the lender if there is a default on the loan. So the lender really has no risk witht he high risk borrower! I have personally seen a 480 Transunion classic score get a 14% APR on a $10k car over there through a reputable lender with nothing down. That never happens!