Unfortunately, there are a lot of drawbacks to working at Carmax. To be fair, this review is based on the location I worked at and my experience. I can't speak for other locations.
For starters, the sales managers at the location I worked at (Pleasanton, CA) are lazy and incompetent at best. They always say to ask them for help, yet never follow-through and never know what's going on. Basically, the majority of your job will be getting them to do their job. It's unfortunate, too—it's almost like they've given up and would prefer to just sit behind a desk, crack jokes, and goof off until payday.
Most of the management has no prior experience in auto sales. Strangely, they take every opportunity to vomit anti-traditional-dealership rhetoric that simply isn't true. This, in my opinion, is cowardly of the management and damaging for new employees who have never worked in car sales before but may want a career in it.
Carmax also has an elementary attendance policy. If you don't have sick time or paid time off and miss a day of work, you accrue a "point". Get six points and you're terminated, no exceptions (unless you're friends with management, of course). It's basically a made-up system that retail stores use to keep their employees under control, and it's pretty bad for people who get sick and don't have any paid time off or sick time accrued.
Another downside is Carmax allows no room for creative problem-solving or independent thought. Everything must be done in a box-checking manner, with no exceptions.
Overall, the company is very disorganized and doesn't value their employees very much. They say they do but always demonstrate the opposite. For example, upon my resignation, the company took about 3 weeks to get my final paycheck to me. They also lost my sales license. When I asked where it was, I got multiple answers. Finally, I was told, "get a new one from DMV. Sorry, don't know what to tell you". This is just poor accountability.
At the end of the day, Carmax wants everyone to fit into a mold and be the same because they want to "give every customer the same experience". There's a major flaw in that thinking. You see, not every customer is the same. Once again, this is a classic example of Carmax treating people as just bodies and not as people.
If you want to work in car sales, do yourself a favor and work at a regular dealership and learn real skills from real professionals. This is merely a retail sales job like Best Buy disguised as car sales.