Jacob points out a fundamental flaw in StoreKit that has been there since it's release with iOS 3.0. StoreKit returns nothing for you to track your payment. If you thought the StoreKit third-party library you were using fixes this, Jacob argues they don't fix the problem at all. Interesting look at what Apple needs to do to remedy the problem.
For a good user experience, your app needs to react correctly to purchases that it initiates, but you can’t.
StoreKit is Broken by Jacob Eiting