You've got to be careful with CarMax but I've gotten a couple great deals out of them. Mainly when it's something slightly non-standard that they can't easily price.

For example, I bought a Jeep Wrangler from them that had both a hard and soft top. Super rare version it seems, that was the only one I'd seen after a year of looking at CarMax, local dealers, out of state dealers, other used car sites, etc. That Jeep ended up being a few grand less than any other one with the same or worse features and even cheaper than many 2 year newer and less mileage ones. It's been mechanically sound for 5 years, so it wasn't a lemon either. It's like having two tops completely threw off their pricing algorithm and into my favor.

The other one was a lot tamer. Just happened to be a car on the old side of a major appearance upgrade and I guess they were heavily discounted because of it. I liked the look of the older style anyway so it worked out for me.