“It appears we just got Banksy-ed": so said Alex Branczik, a Sotheby’s senior director. As The Wall Street Journal reports: Banksy, the anonymous British street artist famous for his eye-catching political spoofs, has pulled a £1 million prank on a buyer of one of his own works. The framed “Girl With Balloon,” a stencil-spray-painted piece from 2006, was auctioned at Sotheby’s in central London. Moments after it was sold to an unnamed buyer for £1.04 million ($1.4 million), the canvas...