In the German rulebook (or is it just me) the difference between chapters and guildhalls is not that clear.
With a Level 2 Trader can you trade from different chapters of the same guildhall or just one chapter?
The entire Guildhall. the guildhall represents your entire collection to the right. It is represented on cards by a white house.
Chapters are the individual stacks within the Guildhall. It is represented by a stack of white cards. If you have to select from more than one Chapter, it will be multiple stacks of white cards.
So to be specific, the 2-card Trader can trade any 2 of your cards in the Guildhouse (even two different chapters) for 2 cards in one opponent's Guildhouse (even two different chapters).
The 4-card level is trading one entire Chapter for one entire Chapter.