That's the premise of a great Wim Wenders' film, The American Friend, staring Dennis Hopper and Bruno Ganz, which is loosely based on Patricia Highsmith's novel, Ripley's Game. Hopper plays Ripley, who makes his money selling "newly discovered" paintings by the late master painter, Anton Kolgash. Kolgash, however, is not actually dead, but living anonymously in an obscure NYC studio pumping out new paintings for Ripley to "discover" every few months, which are then sold to gullible collectors through a German auction house.
I just looked it up. Sounds good. I do like Dennis Hopper though.