If you purchased a smart phone app that doesn't meet your expectations, Popular Science has a guide for how to get your money back. The first thing to try is contacting Google or Apple and explaining why you want your money back. The last resort is complaining on Twitter. One thing not to do is give the app a one star review before you try to get your money back, or you will lose any leverage you might have.
Similarly, the terms and conditions on iTunes and the Google Play Store also include refund requests, although in the case of Apple's store terms are rather opaque. You have to log in to the Report a Problem portal, find the app you have an issue with, request a refund selecting what you feel is a valid and appropriate reason, briefly explain why, and hope it gets approved by the inner-bureaucracy.
Google's policies are a bit clearer, although hedged with ifs and maybes. Within 48 hours of purchasing an app you can request a refund from Google by logging into your Play Store account, going to Order History, selecting Request a Refund on the app you want to return, and explaining why. If you miss that 48-hour window, you have to contact the developers directly.