The owner had purchased the brownstone, the former home of the entrepreneur and trader, Abiel Abbot Low, whose son, Seth, was the 92nd mayor of New York City, for a paltry $2.3 million. And lately, he’d mustered the services of Corcoran broker Vicki Negron to sell it, for $40 million—the highest listing price in the borough’s history. He’d bought a place in Miami Beach and he’d bought a boat. He had hired a man to drive the boat. He also keeps a home in France, from whence Ms. Pinet hails.