I only keep games I feel a special attachment towards, want to keep for replay (or multiplayer) value, or that I can't get much money for. I probably trade in about half of what I buy; maybe more than that, though often I'll have had them for years.
I always keep my games.
I always trade-in my games.
I only trade-in my games if they are awful, boring or if I know I'll never play them again.
I only keep games I feel a special attachment towards, want to keep for replay (or multiplayer) value, or that I can't get much money for. I probably trade in about half of what I buy; maybe more than that, though often I'll have had them for years.