They have thousands of large storage and distribution warehouse and a highway of ships coming and going to china, but they still have it on their shelves when they sell it. Unless you special order it from the warehouse a few miles away. Which still belongs to them and they have physical control of when they sell it. Hell they even have real insurable interest.
You are talking about the way gasoline is sold to the consumer.
But Wal-Mart buys the products they sell in similar methods to the way a refinery buys oil.