title: On Android is it possible to detect if a user bought your app before it became free?
body: <p>We've got an app on the marketplace. It was 0.99c paid, and the user could use it as much as they want. We decided to update the app to run from in app purchases instead, and give the app away for free.</p>
  
  <p>I tried to detect which installs were fresh installs and which were updates by detecting if a previous install had left persisted data behind. This way we could give the older (paid) customers a tweaked app so they got what they paid for.</p>
  
  <p>This failed for an unknown reason so <strong>now we're in the sticky situation where all the <em>paid</em> customers think they've been ripped off and now only have a limited app.</strong> We want to fix this, but we're worried there's no longer a way to discern between paid and free downloads.</p>
  
  <p>If there was a way to tell <em>when</em> they bought the app - that would be enough.</p>
  
  <p>We even considered updating the app with a way for customers to type in their email addresses, so we could check if that user was one of the old paid customers. But apparently Google have taken away the ability to see their email addresses recently.</p>