Kashrlyyk

"The buy/sell box displays a choice if the player wants to buy from the shop or sell to the shop before displaying the shop’s (or player inventory’s) content."

That box contains the ONLY exit button for the shop. After you choose there is no exit button anymore. So how do you leave the shop???

gamingislove

You can use the Cancel input key (defined in Base/Control > Game Controls) to leave the shop, or add the optional back button by enabling Add Back in the type and list box settings of the shop's layout.

pg_ta

Hey! Please press the right control key on the shop's screen.

Furthermore, in order to be able to come out by right-clicking the mouse ...
Base / Control -> Input Keys -> 4: Cancel -> Input Origin -> Mouse
Mouse Button = 1