I have a few things to say and admit. Back when the N64 came out, I was a lot less careful with my games, mainly because I wasn't much of a gamer. I just played a few games here and there, nothing big. I even wrote my initials on some of my Gameboy cartridges (all of which I still own, so I didn't

any used game buyers over with it). But even though I didn't much care for my games, I did keep all of my N64 game boxes in my garage, up until we moved and my dad threw them away. I wasn't very angry at the time, but now that I've become a hardcore gamer, and my Obsessive Compulsive Disorder has gotten worse (literally, I step in patterns when I walk, etc.) I realize that he totally screwed me over for collection purposes. Oh well, I only have 4 N64 games now after getting a few stolen and others I've traded. But the point still remains that I won't buy a game that's not complete. And the same goes for trading. I hate buying games that aren't complete, so I might as well do others like me a favor by trading in my games complete. Hell, I even traded in my DS with everything included (both stylus', Metroid Hunters demo, precautions booklet, etc.).
But then there are other circumstances that cause things to get lost, damaged, etc. Like kids, for instance. I have a little 3 year old brother who gets into everything. Whenever we rent from Blockbuster, he somehow gets ahold of the disks and just grabs them and puts smudges all over it. Before we have the chance to take it away from him, he sometimes throws it for the hell of it. It's annoying, but even if you put it high up they always find a way to get it if they really want it. So the point is that not all things can be avoided. Instead of getting pissed that they don't have a used copy complete, I just take my business elsewhere. I realize that some things can't be bought at most other places, like rare PS1 games, but if it's something you know you can get elsewhere, just leave. If you're really sick of it, buy your games new. It sounds to me like it's important enough to you to pay a few extra dollars to get it new.
Well, that's just my two cents.