Do not buy any antiquity that may have come from conflict zones, like Syria and Iraq
Check with a stolen art database;
Ask about the provenance, then actively check it;
Look at the back of works, outside of their frames;
Ask about forensic testing;
From Michelangelo's 'David' to Van Gogh's 'Starry Night' here are the locations of the world's most famous artistic masterpieces:
Sandro Botticelli, The Birth of Venus (circa 1485/86), Galleria... 