In a purchase/rental model, apps can be demoed remotely, prior to purchase, and only bought if satisfied.
Amazon’s Android Appstore has a “test drive” option that allows remote testing of an app before purchase. It launches a virtual copy of Android in the Amazon EC2 cloud for up to a half an hour for a test of the app. The graphics are exported via a H264 stream. Amazon’s solution suffers from all the difficulties mentioned in section 3↑.