A metric to define the efficiency of the marketing, shortened COS.
COS = Cost / Gross Sales
Depending on the business, it usually varies between 10-50%.
The problem with the Cost of Sales is that it only considers the Gross Sales, not what the merchant earns from its Gross Sales. As an example, discounting drives up the cost of sales but might drive down the bottom line, the operational profit: Net Gross Profit 3