title: in app purchase, how do I know whether a user bought a product (consumable) already?
body: <p>I'm implementing in app purchase.
  Where a user buys a game-like money(a currency a user can use to buy other products with).
  (Many iphone games do this)</p>
  
  <p>Many of these games use the tied apple id(the apple id that a user used to buy the app itself with) for in app purchase.</p>
  
  <p>My questions are.</p>
  
  <ol>
  <li><p>How do these games know the email address of the tied apple id? (I thought it's a reason for rejection of app submission)<br>
  "17.2 Apps that require users to share personal information, such as email address and date of birth, in order to function will be rejected" from <a href="https://developer.apple.com/appstore/resources/approval/guidelines.html" rel="nofollow">App store review guidlines</a></p></li>
  <li><p>After a user buy their currency or an actual product with the currency, they will have to store the purchase information on their server so that the same user can possess the same currency/products in other devices.<br>
  So they will have to store some form of id(the email I guess) on their server. Isn't this a privacy issue?</p></li>
  <li><p>I'd like to avoid forcing users to create separate id just for my app. That's the whole point of the above questions.<br>
  But I also see many apps(with in app purchase capability), and wonder what features drive the app's developer to take a burden of maintainning their own user account information.</p></li>
  </ol>