I'll start with my two recent experiences:
1. I saw a used car on their website that I was interested in, but it was located in another state. No problem, they routinely move cars between their dealerships. Right before officially starting the process, I checked the Carfax report, and it was clean, but one thing jumped out at me - the factory warranty expired in one week. Since transferring the car to my local dealer would take longer than that, I'd be buying an out-of-warranty car, but paying a premium for a car with the warranty. Being clever, I figured I could use that to get them to lower the price. No, I was informed, the price is the price, whether or not the car has any remaining factory warranty makes no difference. I was dumbfounded that they think a factory warranty doesn't matter to buyers. Well, it mattered to me, and canceled the deal.
2. Some time later, I saw another car, again out of state, but CarMax stated that they would not ship it. Because it had all the options we wanted, I called them anyway, asking if there was anyway they could "work with me" to get the car shipped. No, not possible. Period. Okay, so I went on my way, and two days later, the same car popped up in my search results again, but this time, it showed that they would ship it. To say I was annoyed... ugh. Later, curious what happened, I looked into it. Apparently some states do not allow interstate transfer of vehicles unless the owner has title to the car. Okay, fair enough, but you'd think as a money-making entity, they'd have told me that, and said something like, "we've put your name on it and as soon as it's shippable, we'll let you know." Nope, but I over that, really.
Some time later, we sold one of our cars to a local CarMax and I've always been curious how much their markup is. It's been with them for five days now and has yet to appear as available online. Apparently the process takes a while... or maybe a CarMax employee bought it for themselves. Anyway, if and when it appears, I'll update this, as I've never seen anyone post what their car sold for and what CarMax's profit is.