Second-hand makeup is an interesting concept. I’m not bothered by it at all—I’ve bought plenty of second-hand makeup, all the way back to when the mac_cosmetics livejournal community was still a thing, and I still sell things I’ve bought but changed my mind on (usually on Facebook groups or TradeMe).
There are extra things to be cautious of with second-hand makeup, though. It’s harder to guarantee that it’s authentic, and you want to be sure you’ve sanitised it thoroughly before you go whacking it on your face. Conveniently, there’s a site that takes care of all that business for you—Glambot. They buy the products and re-sell them, so you don’t have to mess around with annoying sellers.
I’ve had an account on Glambot for ages, mostly using their wishlist feature to get an alert if a discontinued product I really wanted became available. When they contacted me and asked if I wanted to try a Glambot haul myself, of course I said yes!