Yes it is normal. As @rckoenes said You need to add "restore" button.
If you are using MKStoreKit call this method -
[[MKStoreManager sharedManager] restorePreviousTransactionsOnComplete:^{} } onError:^(NSError *error) {}];
In completion block again check
if([[MKStoreManager sharedManager]isFeaturePurchased:kInAppPurchaseProductId])
So that you can check whether someone already purchased or just pressing restore to get product for free ;)
There is a great video about where and how to put restore button.
In-app Purchase WWDC <- See from 27:30