iOS: GameCenter isn't exactly an app many of us look at very often, but if you play a lot of games, that's where all your high scores go. It sucks when you come across a high score that's clearly not legit, but The App Factor points out that it's easy to report those. All you need to do is launch GameCenter, find the person with the questionable score, tap the three dots icon, then tap Report a Problem. From there, you can select "cheating" and then type in the questionable score. It's hard to say if Apple will do anything about it, but if nothing else you can feel a little better about it.
How to report cheaters and fake scores via GameCenter [The App Factor]