Ensure accurate cost for products to get reliable results.
General
Margin is the percentage of profit made on a product. Themargin
filter helps you to see which products are selling for lower than the desired margin or higher than it.

For optimization, margin column in filtering result is empty unless choosen.
Example
Filtering bymargin
<5%
.

Profit (margin) is only 
The same could be done for products with high margin.4%
, it needs to be increased.