I have my original GSP-15 from 2015 and my Elites from a couple of years ago still. Unless they are already broken, you shouldn't have a problem with buying second hand.
I dry fire the crap out of mine. Broke a firing pin on my second action which was practically new at the time and it was replaced no questions asked. I also bought a spare. My original action has never broken one and I have quite a few barrels through it also.