I know this is a bit controversial, but I sell to buy more, at least I used to. Essentially if I was hunting for games and found a valuable game for cheap I'd buy it regardless of whether or not I was interested in it or already had it. I'd then flip it on ebay, and use the money to fund the purchases of games I actually wanted to keep and play. This was especially valuable when buying directly from ebay, typically games that are either very hard to find in the wild or games that carry with them a very high price tag. he way that I looked at it is if my initial investment in 10 games I bought was $50, and I went back around and sold them on Ebay for $200, and then later bought a $200 game with that money, it was kind of like getting it for $50 since that was all the money I was out.
Honestly if it were not for this tactic my collection would be a fraction of its current size and I'd definitely not have probably half the rarer games I own. On top of that I doubt I'd got into collecting as much if I didn't do this since buying games full retail can get very expensive, at least it is too rich for my blood in some situations.
