When I test the In-App purchase process, I get mixed results.
Sometimes The purchase is successful. sometimes it fails.
Is this behaviour normal for sandbox environment, or should I be worried?
Thanks!
Yes there might be some problem, may below link will help you.
http://www.raywenderlich.com/21081/introduction-to-in-app-purchases-in-ios-6-tutorial
This one includes code for displaying a store.
For more details please go through apple doc