I'm trying a new market strategy so I'm gonna put my 0,79€ App now for free, with an in-App purchase that unlock ALL the contents. I also do not want to betray the users which already has bought it, so I thought to implement a check where who already have bought the App, don't need to purchase the in-App payment to unlock all.
My problem is... can I check when the App has been purchased? Or maybe there is a simple way?