To cheat you, when he generates a block, he doesn't broadcast it. Instead, he runs down to your store...
I think the real danger is that a large mining operator would create a side business selling space in their blocks for these types of intentional double-spends. When they generate a block they could send a text message to a bunch of people saying "try to spend NOW".
I wonder if there's some way to discourage that kind of anti-social behavior; could the network detect that was being done and "shun" that miner's blocks?