Best seller reports on Magento help you find out what were the best selling products in a day, a month or in a year on your website.
Best Seller products can be checked under Admin > Reports > Products > Bestsellers. However, sometimes the reports wont show up and it would turn up only the last months report. To fix this, log into your dashboard, choose Reports > Refresh Statistics. Now choose which reports need to be refreshed. Once you refresh, you should be able to view the reports.