“ When we opened the doors of the first fair, it was quite a shock,” says Amanda Sharp, who together with Matthew Slotover launched the Frieze Art Fair, the now-mammoth annual jamboree of high-end art sales, in a tent in Regent’s Park in 2003. “We were worried because there were huge queues outside and we hated that people were stuck outside in the rain. We thought we had messed up and that everyone was going to have a terrible time.” They needn’t have worried. Visitors happily rolled down the grassy hill artist Paola Pivi had installed in the middle of...