Each time, after making the place absolutely magnificent, they move on. Just don't call Krakoff a house flipper: "I despise that word," he once told the Wall Street Journal. "Design is our life." And so it is with 55 Dune Road in Amagansett, a contemporary beachfront house the couple spent five years building and, two years after finishing the job, have put on the market for $49.5 million.