While public auction sales are declining in the art world, private sales — done behind closed doors between discreet buyers and sellers — are growing. Classic cars are also seeing a shift to private sales, especially with the most expensive and rare models. But its newly formed RM Sotheby's private sales division has seen its sales more than quadruple over the past four years, according to Shelby Myers, global head of private sales for RM Sotheby's. The rise in private sales for classic cars, art, real estate and other markets is being driven by social media, technology and cooling prices for collectibles. "They're leaving money on the table," said real estate broker Noble Black of Douglas Elliman.

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Persons: Robert Frank, Phillips, Christie's, Mark Rothko, Ken Griffin, Ferraris, Shelby Myers, We've, Myers, Patrick Dovigi's, Steve Wynn, Thomas Peterffy —, Douglas, Ernie Carswell, Carswell, He's, Noble Black, Douglas Elliman Organizations: Christie's, CNBC, Sotheby's, Hamptons, Malibu , Bel Air, Beverly Locations: Sotheby's, Christie's, Manhattan, Malibu, Aspen, Palm, Manhattan's Greenwich, Palm Beach, Los Angeles, New York, Eastern, Palm Springs, Malibu ,