You can set your markup in "General settings".
To access "General settings", click on your user mail in the top right hand corner of the screen then click "General settings":
Here you will find "Your markup" settings. The markup is shown in percent. General practice is to set a markup of 10-15% to remain competitive.
Important! To hide the net price on the search form, you must use the key combination "Shift+R". The same combination will return the display of both prices.