You can rest assured that at least one bozo out there will try to game your gamification system — that is, attempt to cheat or to earn points by exploiting loopholes.
For example, suppose you offer a free T-shirt to all users who earn 10,000 points. Suppose further that users receive 10 points for each page view. Users might attempt to game your system by simply clicking page after page after page. They’re not really doing what you want them to do — reading the content, interacting with it — they’re just clicking to increase their points.
Fortunately, you can apply various anti-gaming mechanisms to your gamification system to thwart them. Don’t worry — unlike with matter and anti-matter (not to mention pasta and antipasti), applying game mechanics alongside anti-gaming mechanics won’t cause an explosion. But it will enable you to prevent users from gaming your system.
No matter how smart you are, you won’t be able to predict and defend against every type of exploit of your system, especially in the early design stages. Overthinking the issue at the outset will likely result in a pretty boring gamification system. Just be aware of the issue and give yourself room to incorporate anti-gaming mechanics over time.
You can manually remove points from problem players’ totals and remove problem players from your leaderboards. (That’ll learn ‘em!) You can also set up your system to measure behaviors that are harder to fake — for example, receiving votes from other users.