I'm working on an iOS app and am currently trying to come up with strategies of how to manage in-app purchases:
Android has the nice capability that it caches product ownership information locally on the device and can therefore check ownership without having to prompt the user for a password. iOS, on the other hand, cannot restore purchases at all without asking the user to log in and Apple therefore specifically discourages ownership-checks at app-launch in their Restoring Purchased Products documentation (last sentence of first paragraph).
Now, technically, you can get iOS to provide the same "ownership caching" for non-consumable items as Android does, by just never calling finishTransaction:, except in the case of failed transactions. That way, at every app launch, as soon as you call addTransactionObserver:, you get a list of owned products without a user login request.
Clearly, I can also provide this cache myself using something like NSUserDefaults, but that would be a bit more work and just adds more opportunities to make mistakes in implementing the ownership tracking. And since I need to handle randomly reported transactions from the transaction observer anyways for good measure, I would basically have to implement the above idea and then duplicate its functionality again using NSUserDefaults or such.
Thus my questions: Is it OK to (mis-)use unfinished transactions in this way? Will they ever expire automatically? Might Apple reject my app if they notice that this is what I'm doing? Are there any negative implications of this idea (reliability, performance, wasted memory/storage)?