Pros
I have sold over a 1000 cars for Carmax in my six years of working there and was considered one of the best. I took the job while I was in college and with their help got my degree while working part time. The job paid so well that I decided to go full time after graduation. You will feel proud of what sell and how you sell it. You will also be amazed at how dirty other car dealerships can be and will grow to respect Carmax's best practices even more. I eventually decided to move closer to home and therefore had to leave the company because they didn't have a location in the area in which I wanted to live. If they do come back to my region I will certainly join the team again. The part time job is the best, full time wears you out because of all down time. Get a job there, you will not regret it. You are as successful as you want to be and they certainly give you plenty of opportunity. This is the easiest job in the world for the pay.
Cons
Recently Carmax has started to attempt develop everyone into a World Class Sales associate, and the training never stops. They do this because they hire almost anyone. The bummer is not everyone needs to be trained day in and day out. Their business model is so easy to master and the process of selling a car is so repetitive I find the training counterproductive. It is easy to get promoted into management, but that is as far as you most likely will go, successful managers with 12 plus years experience are still waiting to get their own GM positions and won't because they primarily hire that position from the outside. Get comfortable.