Here are a couple of comments about Carmax,
My local Carmax in Glencoe IL will let you test drive on the highway if you ask. If they refused I would have asked for the manager. I personally would never buy a used car that I did not test drive on a highway.
The background check available from auto check always caries buyback protection. Did you view the Autocheck vehicle history report? They have to show it to you, it's Carmax policy. Autocheck will buy back the car from you if they miss something like that. This is like title insurance on your home but the buy-back protection is from Autocheck not Carmax so you have to go to them.
As for the scratches and water spots, Carmax, like most used car dealers, sells WYSIWYG, What you see is what you get. Since all Carmax cars are washed over and over if you are buying a car with spots and scratches then you are buying a car with spots and scratches. There is no warranty on cosmetic damage. It is what it is. So do your due diligence before you buy and never expect anything cosmetic to be repaired after the sale unless you get it in writing signed by a manager. This is true with any used car at any dealership.