One of the recurring claims from dealers and auction-houses in the last year is that those from outside 'the trade' are spotting toxic antiquities. Members of the trade need to examine is why their due diligence searches are not picking up this material. Are they placing too much confidence in searchable databases? Are they aware that these databases will be unlikely to pick up archaeological material fresh out of the ground?
But then there are the other clues. For example, if the personal name on an Egyptian relief is linked to a known tomb in Egypt, it could be worth checking the publication. If the vendor of a group of material appears in published lists linked to the "Medici Conspiracy", then it is worth checking the material a little more carefully. If an object is similar to material that has been returned to Turkey, then ensure that the collecting history can be authenticated. If a lot is linked to a dealer known to have handled material whose collecting histories are suspect, then dig a little deeper.
The appropriate response from the members of the trade is to improve the rigour of their due diligence searches and to work with members of the academic community to protect our universal archaeological heritage.