There was a similar subject here
Okay. We can find out about user's purchase using RESTORE_TRANSACTIONS request to Google Play. But. It is written in documentation that " You should use the RESTORE_TRANSACTIONS request type only when your application is installed for the first time on a device or when your application has been removed from a device and reinstalled." Why not after every start? It looks comfortable and possible to query Google Play every time when the app starts.
Otherewise
1) I should store information about payment on my WEB server
2) Or I should save this info to sdcard. The record should be secure, including device ID, so that copy on another device will not work
So. Which way is better? Thanks.