Quoted from VolunteerPin:2. Don't get caught up in the 'have to have it now' mentality...it WILL cost you
That's a tough one. When I started, I passed on some titles I recently picked up, as they were going for $1000-$1,200, and someone wanted $1300-$1500. I thought it was the smart thing to do at the time.
Flash forward, and I'm now paying $2,500-$3,000 for these same titles, and that's IF I can find them. My honest opinion on this is buy them all and sort it out later. Take that with the obvious grain of salt being don't go broke or piss your wife off (too much).
They are easy to sell, and having trade bait puts you in a better position anyway for something you want. There is the flip side to that, being the crazy over the top prices for a game you just have to have now, but sometimes we gotz to do what weez gotz to do!
Again, the classic argument: they keep their value, so it's hard to make a bad decision. There is usually more bad decisions "felt" with ones you sell without really thinking it through.