In most housing markets, a listing price gives buyers a reasonable starting point. In Darien, Connecticut – a town of roughly 12 to 14 square miles on the Long Island Sound, about an hour by train from Grand Central – it has become something closer to a floor in an auction. Homes routinely sell well above asking, sometimes by hundreds of thousands of dollars, and the pattern has persisted long enough that buyers and agents can no longer rely on list prices as meaningful signals. The cause is straightforward: demand consistently exceeds supply in a town with roughly 6,300 households...