I hear ya on that (trading / selling).
Aside from GHIII, GH: Metallica and GH: Aerosmith, I've sold about 95% of my other games from my PS3 on Amazon.
The only games that I think that I have left on PS3, aside from those 3 are Resident Evil 5, Darksiders and MK9.
MK9 I will hold onto for collection purposes, but if someone makes me an offer for the PS3 and / or the 2 other games, it's sold.
I'm not a console hoarder.
The only console that I've made that exception for and have kept from my childhood was my Sega Genesis (and it's still in perfect working order).