Thrifting can be a good way to find some rare and gem items that you never see. Several of the items I am about to list, I have seen once, or only a few times in my life (And these are just the very big/rare finds), so I had to buy them for the ridiculously low price.
Fire Emblem: Path of Radiance - Gamecube - $5
Team Buddies - Playstation - $3
Elder Scrolls II: Daggerfall (Complete in Big Box) - $5
Now, being the big fan of the Gamecube that I am, will occasionally shell out some money to pick up some extremely rare titles. For example, last week I saw Skies of Arcadia: Legends for $80. I had to get it, it was the first time I had ever seen it in person. Also, several years ago, I saw an Australian version of Pokemon Box for $65 on eBay. I had to get it, it was the first time I had seen the Australian version, and I have never seen another listing like it.
A lot of things do happen by luck or chance though. Right place, right time kind of thing. It's all about being ready, so that when those times come, you can get the game you want.