I've bought a couple of vehicles from them over the years and it's always been a fantastic experience! I'd gladly pay a little extra to not have to deal with sleazy dealers and their antics.
CarMax has a 24-hr test drive option and a 30-day return policy. So, if you don't like it, just bring it back and they'll unwind the deal. I bought a Corvette from them about a year ago, put about 600 miles on it, decided I didn't like it, and returned it. I thought for sure it'd be a hassle, but the manager just took the keys, recorded the mileage, had me sign some forms, and that was it. No pressure at all!
Plus, I've heard good things about the MaxCare warranty. Obviously from the Doug Demuro Range Rover saga. But also, my mechanic says they're pretty easy to work with. So, I'm willing to buy the warranty.