Buying a home on certain parts of Nantucket is a gamble. One businessman regrets it, calling it a "terrible investment."

This summer, a few months after he’d purchased a precariously situated Nantucket beach house for $200,000, Don Vaccaro, the founder of ticket-brokering business TicketNetwork, acknowledged in an interview that while the house was, at least to him, an irresistible bargain, “everyone knows these houses are going to fall into the sea.”