I have never sold a single game and I hope I'll never do. I love collecting stuff and even though I have some games twice on different platforms(Portal 2 Steam and PS3 physical, Demon's Souls physical and digital courtesy of PSPlus, Zero Escape: Virtue's Last Reward physical on 3DS and digital on Vita courtesy of PSPlus again, Dragon's Crown Vita physical and PS3 and Vita digital PSPlus, Modnation Racers Road Trip physical and digital PSPlus, NFS Most Wanted Vita physical and digital thanks to EA being nice for once. I could go on and on.) I don't want to trade them because I love seeing the boxes and the sensation of having something physically to properly say "I have it". In fact, I bought Tales of Hearts R digitally when was on sale some weeks ago, but if I see an opportunity(Tales of Hearts R is a Gamestop exclusive, in my country there are no Gamestops) to purchase it physical, I'll do.
That being said, if my monetary situation gets bad and I have to, I'll have no choice but to sell the dupes.