They can find a rather mean letter from a Venatori named Volaris to an underling named Latifan admonishing him for sending Volaris a load of junk. Just because an old book or artifact was owned by a dwarf doesn't mean it's worth sending, he is interested only in manuscripts or artifacts that are either (1) both (this is underlined an insulting number of times) ancient and (again) dwarven, or (2) recent dwarven research materials, and he should search the house again because he must have missed something like the bumbling idiot he is. Dace (which they can determine is the name of a wealthy surface-dwarf merchant who owned this manor) cannot have gotten everything out before they arrived.