Listening to MacBreak Weekly (ep. 101), they were discussing that there is no way to try before you buy on apps in iTunes AppStore. They seemed to skirt around the solution without actually saying it.
For those apps where try before you buy is an issue, a free or discounted version should be made available which demos the features, with a premium version at the ‘correct’ price. This is back to the old fashioned shareware model, or the modern model of freemium which is more typically applied to products and services.
This would be an ideal working model that allows a test drive on a trial basis with very little or no outlay. It is a model which is proven and accepted.
This model is also a great way for a developer to determine whether there is an audience for a product. By releasing a basic version of an app for free or low cost, the response to the app can then be judged to inform the decisions on the direction of the product. By soliciting feedback on feature requests, improvements, enhancements and third party integrations it is possible to build for the current userbase.
This allows a developer to test the market before making a huge commitment to a project that may not offer the required return.
For both developer and user, the AppStore could prove to be a win win situation.