product_sales not lining up with number of orders

Hi,

This number is incremented each time an order is created. And it is not updated when orders are cancelled / deleted. It is a column of data you can user to roughly sort the products based on the sales on the frontend, to be able to get a "best sellers" products listing. But you can't use it as an accurate source of reporting.
Mass actions and the reports in Orders>Reports on the other end base themselves on the actual orders, based on the statuses, etc so they provide accurate data.