If you use the reports that are available across your seller account --Business reports, Order reports, Payment reports, and so on-- you may notice what seem like discrepancies. This is because the various reports are set to pull slightly different data based on the service the report is set to perform.
Here are just a few examples to illustrate these differences:
Business reports takes into account cancelled orders, while Payment reports do not.
Settlement reports include Amazon fees, while Business reports do not.
Business reports by ASIN and the Orders report in Manage Orders include all orders placed during a certain time period, regardless of settlement status. Payment reports include an order only after it is shipped.
Seller Performance in Business reports by date looks at refunds in terms of the unit refunded. For a unit ordered in September and refunded in October, the refund counts for October. Customer Metrics looks at refunds in terms of the order. For a unit ordered in September and refunded in October, the refund will count for September.