Back in 2003 I came across a clutch of Conker Bad Fur Day brand new at a Meijer store for $5 each. In my own stupidity I only bought one. The worst part is that they stayed there for quite a while and I saw them nearly every time I went to buy groceries or something. About two years later the same thing but copies of Document of Metal Gear Solid 2, but I did the same as I did with Conker (bought one for $5 and ignored the rest). I still think about that stash every now and then.
hindsight is 20/20, no real way to know what the market was going to do at that point. just think, the exact same thing could be happening every moment you go out to a local game store or thrift store.
edit: just over 40 games into cleaning my N64 collection, a large number of these have the gold plating rubbed off the contacts
including conker's bad fur day. no other expensive ones are bad yet though, battle zone, big mountain, donald duck, and bomberman 64 the 2nd attack are all fine luckily.
also came across 12 that had bad enough problems with the box, manual, and cart that i decided to pull them from my collection to sell and replace completely. at some point years ago i had picked up a fair chunk of CIB n64 games from a video store, so i'm expecting there to be a fair number that are far below my standards now.