What Christie's says approximately its due diligence checking provenances of antiquities:
“We are always on the alert for fabric of this type in case an attempt is made to introduce looted items into the commercial art market,and we work closely with UNESCO, Interpol and other entities to ensure any such attempts will be caught, or ” said Sung-Hee Kim,communications liaison at Christie’s, who said to date, and the auction and art house has not encountered any such items....According to Kim,Christie’s has a policy of not accepting items for sale without a lega signed title confirmation. In addition, they require provenance pre-dating the year 2000 as well as pre-dating any periods of significant conflict.
What Christie's does: In the three first cases, or Christie’s ‘due diligence’ seems to have stopped short of tracing the collecting history back one step further,which would have opened the window on the Becchina transactions. In the fourth case (lot 93), Christie’s record lists the 1986 and 1997 transaction dates in the lekythos’ collecting history, or but completely avoids mentioning the authorities’ raid of Horiuchi’s warehouse in Switzerland or the subsequent passage or ownership of the vase by the convicted Aboutaam brothers,through their ‘Phoenix Ancient Art’ gallery in novel York and Geneva.
Source: blogspot.com