I am looking at 2015 - 2018 Avalon’s with less than 100,000 miles, not a hybrid. Are there any years I should avoid? Is there anything special that I should have my mechanic look for?
Those are excellent vehicles. Check out the links below for more information on common problems. You would want to do a bumper to bumper check of everything but as for common problems up to around 2016 they had some oil leak issues with the VVT-i systems. This wasn't as big an issue in the later years.
You can find many good links on google,
https://www.motorbiscuit.com/the-toyota-avalons-disasterous-debut-is-its-worst-model-year/
https://www.youtube.com/watch?v=QpF9I1YFGxo
https://repairpal.com/toyota/avalon
All in all, this generation of Toyota Avalon is relatively trouble free if you take care of it. As always, the later years of the generation would have less problems than the earlier ones. Remember to have a mechanic check out the car you are planning to purchase to make sure you aren't buying someone else's problem.
Ideally, get the newest you can afford. 2018 MY was the last year of that generation, and if within your budget I’d get the 2017/2018. But overall that generation (2013-2018) was pretty solid when you compare with the competition.
Also, in general cross-check the vehicle you are interested in with our Toyota/Honda Common Problems Sticky under our Car Buying Guide:
