While reports like the Sales & Shipment Report are the most commonly used in the suite of reporting offered, the Returns & Received Inventory Report can be useful if you want transparency on all activity on the store including what is being checked in and subsequently returned.

RECEIVED INVENTORIES REPORT

If you would like to monitor shipments into your inventory set you can do so by viewing the Received Inventories Report.  This report will include items checked into inventory (broken done by SKU) as well as returns coming back into inventory. It will include the number of boxes in the shipment as well as the receiving time (in minutes) it took to count the items and check them into inventory. 

RETURNS REPORT

This report shows all orders that have been returned. It will include info about the product returned (product name, SKU #, qty returned, return value) as well as the reason for the return if one is provided by the customer. 

Please view this article for how to access reporting.