False provenances are needed to insert art forgeries into the historical record.
Where there is forgery there is false provenance.
Dealers who sell forgeries are great sources of false provenances. A special kind of writing is involved in the creation of false provenances. A talent for making things that are not true seem at least plausible.
Question: Do dealers of forgeries also sell looted art?
Some, like Knoedler, are known to have sold both at one time or another. Knoedler's prestige and power enables it to insert lies into the historical record without being challenged for a very long time.
What about the others? How to find out?