Dirty cartridge and a sticker on the label. Off to a great start.
So, we've got a nice and dirty copy of F-Zero X that came from Goodwill for $3, and a copy of Jade Empire Limited Edition that's in great shape and only cost me $5 at a used game/movie/music store. We'll be consulting two things that should be in every collector's cleaning cabinet; Mr. Clean Magic Erasers and Goo Gone.
Usually around $5 each.
We'll start with F-Zero since it's pretty obvious how to use Goo Gone to handle stickers.
Thankfully, the price sticker peeled off without doing any damage to the label. It is possible to replace labels, you'll need some kind of sticker paper and a good scan of the label. I haven't replaced anything as large as an N64 label, I've done it for a Game Boy game and a DS game, but as long as you're working with a high enough resolution, it will look nice.
If you are printing out a replacement label, don't be a jackass and use scissors. Get some kind of paper cutter to make a nice straight edge. Once I had the label cut out nicely, I used some sort of tape that isn't very glossy and is relatively thin and also large enough to cover the label with one piece. This gives it a more retail look, and protects the label from getting dirty. I've only done this twice though. There's probably some kind of sticker paper you can buy that has the right level of gloss to it, but my tape solution works really well if you can find the right type. For the two I did I can't even notice the difference.
It's a lot of work, so really you should just not buy games with fucked labels. Anyways, get that Magic Eraser ready and start scrubbing away at the dirt and shit on the cartridge. Don't get too close to the label, it'll wear at the paper since the erasers are gritty and sandpapery.
Almost like new.
And there we have it! Just a few seconds worth of scrubbing and it looks great. The label is a little bit dirty, it's hard to tell from the picture. The rest of the cart looking better makes it less noticeable. I'm not bothered by it. If a label is sort of dirty, you can't really do anything about it short of replacing it. The pins were a little dusty, so I just ran a Q-Tip over them to clean them up a bit. This is important, because DON'T BLOW IN YOUR FUCKING GAMES. Seriously. I never blew in any of my cartridges, and they all work perfectly today.
Anyways, on to the next one. It's important that you take EVERYTHING out of the DVD case. Goo Gone is very oily and it will spread all over the surface of whatever you put it on. Don't leave the insert in the case. Nothing. Everything out. In case you're stupid, it looks like this.
Then, drip some of the Goo Gone onto the sticker. This was a really old sticker, so it was on there pretty well. I think it said Electronics Boutique, either way, this is the really old style of used sticker that EB and Gamestop used and I wouldn't be surprised if it had been there since 2005. The Goo Gone will soak into the sticker pretty quickly, and you'll notice that oily shit goes everywhere. If the sticker is at all close to the top of the case, it'll go in-between the sleeve and the case. It's impossible to avoid.
Once you've done this, let the case sit with the Goo Gone on it for about 5 minutes. Come back to it, and it should peel right off. After you've done this, you'll notice that the Goo Gone is basically fucking impossible to take off with paper towels or an actual towel or anything else. After I've hit the case with some Goo Gone, I usually was them off with water in the sink and then dry them thoroughly so that there's no trapped water to get the sleeve or manual wet when I put them back in.
After that, admire your work.
Simple, quick and looks a hell of a lot better.