 Sotheby's is defending itself at a federal court trial against accusations that it participated in the defrauding of a Russian oligarch out of tens of millions of dollars for works by famed artists like Amadeo Modigliani and Leonardo da Vinci.A lawyer for the auction house told jurors Monday at the start of a Manhattan federal court civil trial that the oligarch, Dmitry Ribolovlev, has only himself to blame, the lawyer says Ribolovlev trusted an art dealer who bought art from Sotheby's and resold it to Ribolovlev at inflated prices. Ribolovlev's attorney told jurors Sotheby's was part of the rip-off.