We were also looking for a late model S to buy prior to getting our Model 3. I had a couple of VIN #,s to check out and compare the options included so went to the Tesla store where the staff were very helpful.
Then they asked me to go online at the store and build our ideal S. Then they showed me that, after discounting for the rebates, we would have only saved about $20-25K by purchasing a used Model S. By spending the extra money we would get a brand new car with full warranty rather than one with 40-50K miles on it. Plus we got AP-2 with FSD rather than AP-1. My wife and I talked it over and decided to just get a new one.
When asked by our friends and neighbors why we spent so much money on a car we just tell then that this is our "Motor Home". A lot of our friends, and even a few neighbors have Motor Homes and do not use then that often. We use our Tesla Model S every day, and take lots of medium and long distance trips throughout the year. Over 15,000 miles in our first 3 months. After nine months we are over 21,000 miles and our next trip season will start again in April.
Think about this before you purchase a used Model S for over $50,000. Oh, and I am happy to give you my referral code, lol.