I've complained about the lack of app trials via the mac/iOS app stores for years now. It would be SO EASY for them to incorporate this functionality for developers to allow, where I can try a full version of an app for a certain amount of time and then it would lock me out until I purchased it.
Not having that feature has easily stopped me from giving at least 50% of apps I've found a shot simply because I don't want to make a blind purchase based on 5 screenshots.