I think @Bigriver often has some useful advice concerning Model S's in that timeframe.

 

Do you have a specific one that you are considering? What about the year 2016 and the 90 battery has you most interested?

In general I think Tesla had evolved the cars by 2016 such that they are a pretty solid car. I used to hear complaints that the 90 battery was degrading faster than the 100 battery that came after it. I don’t know any data on that, and can’t say that I’ve heard that complaint for awhile.

October 2016 and later had AP2.0 which is upgradable to HW3.0 for FSD. That would be important to me. Do you care about that?

I often hear people shopping for older model S’s in search of free supercharging that stays with the car. Is that something you are wanting?

Teslas today have a lot of features in the base version and there are few options. In 2016 they were more alacarte. For example, my 2017 model X does not have a heated steering wheel while most from that vintage do have one. So if comparing different cars from 2016 (or before 2018) be aware of the different features they may have.

And finally, 2016’s are done with the battery and drivetrain warranty. Both of those are very big costs if they fail. Are you ok with that gamble?