Newbie needs help - how to sell items/ scrolls

[Makonar]

Sorry, the interface is not intuitive for me and I do not know how to sell items/ scrolls...
right click lets me drop, use or get info.
Drag and drop doesn't work in castles...
traders offer me to purchase monsters, scrolls and items, but no selling option is clear to me... please help
how, where and when can you sell items and to who?

Also - can't find in on the hint's forum... hod do you trigger the rage spirits? People seem divided to those who know and those who don't know, some talk of boxes, but it is still unknown to me...