When user B uses the device there is nothing telling your app that it is not user A.
Your app could require that the user (A or B) refresh the receipt. Depending on how long ago the last user interacted with the app store, that MIGHT require that the current user log into their account on the app store. That WILL require a log in if the last user logged out of the app store before handing the device to the other user.
Your app could require that the user log into your server each time they want to use the app.
Or you could forget about it.
This was a long ago, still I am curipus if you found any solution to this problem. Please share your thought on this.