A sell will register:
We can set the selling price of each book, and also choose a client discount (5% or 30%, but those are customizable).
We can also choose a place to sell from. In that case, the interactive search will suggest titles that are present in this place.
If we don't choose a selling place and the card is present in both a place (our stock) and a deposit (not ours), then the sell of this card is ambiguous. Currently, Abelujo chooses to sell the one in stock.
updates: the behaviour changed in version July, 2020). Previously, we had to specifically choose the deposit with a menu.
It is possible to undo a sell. Just go the History and click on the cross icon in front of the sell you're interested in.
See the History section.