the sibling comment to mine references a huge volume of pop-tarts being shipped to florida in preparation for a hurricane. if during mid-shipment the weather changed, wal-mart would call up the supplier, cancel the order, and all the trucks would return the pop tarts to their suppliers at no cost to wal-mart. with pop tarts it isn't such a big deal because they don't spoil, but farmers who supply wal-mart will get shipments of spoiled produce returned to them if wal-mart decides they don't need quite as much volume that week. and they just have to deal with it, because they can make more money getting screwed by wal-mart than they can selling to ethical companies.