Is there a solution to the following method of stealing something from retail (groceries, coffee, a TV, etc)?

The owner of BTCGuild walks into a store and selects something.  He goes to the cashier who accepts bitcoin.  He hits send, the cashier sees the transaction (the "spend transaction") and says "thank you", and the miner walks away.

Now, there have been no confirmations on that transaction yet.  As this is retail, the cashier can't have the customer waiting around for a block or 3 to get written.

The miner kept a log of the spend transaction and knows exactly which bitcoin he spent at the store.  When he logs into the pool operating software, he attempts to write a different transaction (the "steal transaction") to send this bitcoin instead to a different address (a double spend).  Since this is the owner of BTCGuild, he's able to write the next block 30% of the time and successfully steal from the store.

The best part about this is that in the 70% of the times when some other miner writes a block, and the spend transaction is written to the blockchain before the steal transaction can be written, no one knows that a theft was attempted.  The steal transaction never gets propagated on the network until it gets written to the blockchain.

Someone knowledgeable please tell me there is a solution to this.  How could retail trust bitcoin if miners could sometimes steal from them?