I've sold all of my games. I buy and sell them for a living. I get sick of games pretty quickly anyway so there's no emotional attachment to any of them. My brother recently game me his entire collection, which was made up of hundreds of different games, and now I have to go and sell those. I only sold about fifty from his collection so far.
I've sold a lot of games recently, dating back to XBOX Classic games really. I'm in the process of moving house so any space I can gain counts (and of course, getting some extra money in my pocket is always a joy to behold) but I'm not doing anything 'special' with the games as I'm just popping them into my local used games/DVD store but hey, every little helps and I hope someone else gets to enjoy the games I've had!
It's almost impossible to sell a digital game unless you have an unused CD key. A lot of sites sell those tho at considerable discount. I got COD Black Ops 4, just a key, for $22, and redeemed it with Blizzard without issue.
I have a ton of games from the ps2, ps3, xbox360 and some on the ps4, I do think about selling them but prob not worth a lot tying to sell individually, maybe a job lot but i think if i do will try and sell at my local cex store.
When I was a kid, I traded in games towards other games. I've had to sell my Xbox One and Switch back in February before I got my new job because money was tight. I still need to replace my Switch I replaced my Xbox One already though.