Amazon's first-leg calculation should be considered an expense, because the cost of the first leg includes multiple fees such as transportation, insurance, and customs clearance. These fees are incurred to complete the import or export of goods, rather than costs directly related to the production or manufacturing process of the goods themselves.

In addition, the first-leg fee is usually handled by logistics companies or agents, rather than being paid directly by manufacturers or sellers. Therefore, Amazon's first-leg calculation should be considered an expense.