I just sold mine (a 2013 85), so a few things come to mind.
- The ESA (Extended Warranty Agreement). If you want it ($4k), and the car doesn't already have it, then the current owner will need to buy it, and transfer it to you ($100 fee). As the second owner, you cannot buy the ESA yourself. Many don't see much value in it, but it's a personal thing
- obviously check Carfax for history and so on. There's a lot of S's on the used market now, so there's no need to take one that's been in a wreck.
- Every buyer asked me what my battery degradation was. Nobody can really answer that as Tesla changed the charging algorithms several times, but the general consensus is that it's trivial. Potentially more significant is how often the car was range-charged, as that will have more of an impact on the battery.
- I had a NEMA 14-50 at the start, as the HPWC was in short supply. It just means you have to use the portable charging cable (and buy the 14-50 adaptor), which quickly becomes a PITA. Since the HPWC is cheaper now, I'd never use anything else.
I can't really talk to the price....seems a little steep to me based on age and miles, but I've not paid a lot of attention to the P85+'s.