This is very hit or miss based on market and location. CarMax was a huge pain in the ass (and rude) for me. I called ahead of time asking if they could give me a ballpark estimate since I'm 150 miles away from the CarMax location, I also asked about COVID issues and if I had to go in person for an estimate (this was August time frame). The lady insisted that they only do in person estimates and I HAD to have someone walk around the car with me. She also assured me that they are very close to KBB amounts and if I looked it up on my own I was know basically what they would offer.
I trek up the 150 miles during the great PNW fire season with smoke all over the place and low visibility, as soon as I get to CarMax I'm told to please go back to my car and wait and TAKE PICTURES OF THE CAR AND SUBMIT THEM VIA EMAIL. It would be a non-contact appraisal due to COVID. I WAS LIVID that I drove 150 miles to snap some pictures of the car in the parking lot and email them to CarMax when I called 12 hours earlier and was told I HAD to be there in person.
CarMax came back and said my whole front end needed painted on my 2019 SR+ with 7,000 miles (and paint protection film). I emailed back and said I disagreed because they were bug splatters from driving 150 miles to get an estimate and they said it still looked bad enough that they would repaint. Well I stormed back in and dragged out a rep to look at the car in person who finally came out but said "repainting the vehicle doesn't really affect your estimate all that much,", he glanced at it and said "ya, looks like it needs painted... I was floored and told him to get closer or put glasses on because they were bugs!" he finally steps about 2 feet away from the car and goes "oh ya, those are just bugs, they'll wash right off!" but then assures me the estimate would remain the same and there wasn't any reason to resubmit it because "painting doesn't change the price we'll offer."
I think they offered me like $28,000 for a 1 year old Model 3 SR+ with 7,000 miles on it. Vroom offered $35,500 sight unseen and Carvana offered $38,900 but I would have to drop the car off in San Fran. I was furious with CarMax and drove back home after 15 minutes of being in their parking lot taking pictures of the car and fighting with their sales guy that bugs didn't mean the front end needed repainted.
I got MASSIVE "used car" vibes from the place. It reminded me EVERYTHING I hate about the car buying process and how much more I love the Tesla process of click, email back and forth a bit, and buy.
Vroom was rather slow (two weeks start to finish) and required a couple calls and emails from me to poke and prod to get documents emailed out faster, but it was 1,000% better experience and didn't make me feel sick and dirty from the sleazy used car sales man tactics and atmosphere.
Again, likely market specific and probably time specific, but do NOT just go there and hand the car over before you get a couple other quotes, and frankly, I would make them my last resort not my first.
