Margin

The difference between the selling price and the purchase price of a product; margin determines the profit from the sale. 

Margin determines the profitability of the goods and services you offer. Reducing margin is also a practice commonly used by salespeople during their commercial activities.

Read also:

1. Up-selling

2. Cross-selling

3. Sales forecast 

Useful links:

https://pl.wikipedia.org/wiki/Mar%C5%BCa

https://consider.pl/marza-wszystko-co-powinienes-wiedziec/

http://www.poradnikhandlowca.com.pl/wsparcie-sprzedazy-artykuly/jesli-chcesz-zarabiac-pamietaj-o-marzy