I have purchased two through Carvana. The best purchase experiences I have ever had, by far.
After shopping the website for a few weeks, I found something I wanted. It took about 20 minutes online to start the process. I finished the online stuff around 11:30 pm. When I woke up the next morning, I had an email waiting that said everything was approved and set up and confirmed my selected delivery time.
Truck showed up on time, and delivery person was very helpful and nice. I looked the car over, and took it for a quick test drive. It had a slight mildew smell, but I wasn't overly worried. The smell got worse over the next day or so, so I called them back about returning it.
The return process was equally painless. I called on a Saturday morning. The lady asked if I wanted to return it for refund, or pick something else. I told her I wanted to pick something else. She asked if it was saved in my favorites, and when I confirmed she had the correct vehicle, she asked me a couple of questions about warranty and delivery vs vending machine, then confirmed my new delivery time. She apologized that they couldn't get it to me until mid day on Monday.
Driver showed up, unloaded the new one, which I looked over and was very happy with, then loaded up the old one. Took 20 minutes or so.
I could not be happier with the experience.
I bought another one from them last week that was delivered Saturday. The experience was exactly the same.