You're right but again, blockchain is not needed for that part either. Just have wallmart publish their signed database publicly at regular intervals this way if they cheat and try to modify existing records anybody with an old dump could prove that something weird happened (since the database is signed simply showing a conflicting entry with a valid signature would be enough to demonstrate that either Wall-Mart did something fishy or that they got compromised. You wouldn't have to trust the whistle blower).