Yes! There actually is a way to try out any app before you purchase it. All you need to do is to step into the Apple Store and a ask for the particular app to try.
Apple has not been publicizing it, but this method seems to be existing. Trying Apps can be easy when there’s a lite version of the app in the App Store. But what if that Lite version is not available? Visiting the Apple Store seems to be the only way.
The other way round (But not recommended) is to purchase the app and then get an innocently purchased app refund. But this might take some time.
The Apple Store guys are really customer friendly that you can even request the app you want to try. May be they are not charged for purchasing apps? I’m not sure! :D. This is just a tip. I heard that this has been happening in the New York Fifth Avenue store.
If you are too lazy to just go to Apple Store and try it out, go ahead and purchase the app you need and then get it refunded.