In 2005, Maspro Denkoh awarded a contract to one of these institutions based on a game of rock, paper, scissors. Citing patriotism, Cai Mingchao "sabotaged" a 2009 event held by one of these institutions by refusing to pay. A collusion scandal between the largest two of these institutions spanned most of the 1990s and implicated A. Alfred Taubman. That near-duopoly of these institutions has crowded out smaller ones like Philips and Bonhams. A format (15[1])of events held at these institutions called "mineing" is similar to ones held by the (*) Dutch. Hobby Lobby sued one of these institutions headquartered on London's King Street for providing false provenance of the Gilgamesh Dream Tablet. An event held by one of these institutions made Salvator Mundi become the most expensive painting ever sold. For 10 points, what institutions' largest examples are Christie's and Sotheby's? ■END■