Due diligence and the auction houses

I have discussed earlier this year the issue of due diligence and what auction-houses could do when objects are identified from seized photographic archives (April 2011). I have also addressed the issue of whether or not the Italian authorities should release images that were seized (June 2011).

Auction-houses are quite capable of conducting their own due diligence searches when they are alerted to potential problems (April 2011). Some choose not to do so.

So what are the issues:
a. Are buyers provided with the full and accurate collecting histories ("provenance") for the objects they acquire?
b. Are buyers alerted to potential problems over disputed ownership?
c. Who are the anonymous vendors?