My co-researcher Christopher Chippindale observed:
the corruption through looted objects is so deep and wide and long-lasting that even people of good character who bought things decades ago may inadvertently have acquired illicit stuff.
How can such material be avoided?
Museums and private individuals need to have a rigorous due diligence process. Was the object known, i.e. documented, prior to 1970? How reliable is the information?
The acquisition of antiquities requires more than "good faith" or a reliance on "good title".