How Do I Get A Refund From The App Store?
In most cases, all sales are final on the App Store but you can still attempt to get a refund (which may or may not work). Go to your account in iTunes and click on your Purchase History then click "See All". Look for the button that says "Report a Problem", click on it and then select the app that you want refunded. You then have to write a detailed plea explaining why you deserve a refund. Reports are reviewed on a case-by-case basis so there's no guarantee that a refund will be granted.
UPDATE: As of December 2014, EU users can take advantage of a 14-day no questions asked return policy for purchases from iTunes, App Store, and iBooks purchases.