Anybody with a better understanding of filecoin - can you explain how the protocol can tell the difference between a legitimate hardware failure and a storage miner who stores the uploaded file, signs proof of replication to the blockchain, then immediately deletes the file so that he can "store" more files, collecting more payment, and then refuse delivery upon download request, claiming hardware failure?

Does the blockchain have some way to prevent miners from double-spending their storage space? Is payment only collected upon retrieval, allowing Filecoin to be abused for storing backups that are rarely retrieved?