It's tough selling a paid up front app on the App Store. Users have no way of knowing ahead of time whether an app will fit their needs or not, and no one wants to spend money on an app only to find that it wasn't what they expected. Fortunately, App Store review guidelines have been updated this week to address that problem. Matthew Humphries reports for PCMag:
The updated guidelines state that, "Non-subscription apps may offer a free time-based trial period before presenting a full unlock option by setting up a Non-Consumable IAP item at Price Tier 0 that follows the naming convention: "14-day Trial." Prior to the start of the trial, your app must clearly identify its duration, the content or services that will no longer be accessible when the trial ends, and any downstream charges the user would need to pay for full functionality."
So users will know before they start using an app that it will cost money, but only after X days of free use. The upfront transparency should prevent any user frustration, but it could also greatly improve the quality of content in apps because the developer really needs the user to reach the end of the free trial wanting to pay to continue using/playing.
This isn't necessarily a change of policy, but more an explicit clarification of something that's already been allowed. The Omni Group, for example, began switching its entire suite of apps in September 2016 to the same sales model: free downloads, with In-App Purchases for unlocking full functionality after 14-day trial periods. Since that time, however, very few apps have followed the same path – likely in part due to continued uncertainty regarding what's officially allowed. The updated review guidelines should lead to a welcome increase of paid up front apps transitioning to free downloads with In-App Purchases, thus enabling more ubiquitous free trials across the App Store.