What should happen when non-purchased user press the restore purchase button in iOS?

You can check if the queue has any returned transactions, and if not it means that there are no purchases to restore:

func paymentQueueRestoreCompletedTransactionsFinished(queue: SKPaymentQueue!) {
  if queue.transactions.count == 0 {
    let alert = UIAlertView()
    alert.title = "Oops"
    alert.message = "There are no purchases to restore, please buy one"
    alert.addButtonWithTitle("Buy")
    alert.addButtonWithTitle("Cancel")
    alert.show()
 }
}