Bill Van Keuren shouldn't have had any trouble selling his family's house. It's a three-story colonial with a formal dining room, thick mahogany doors, leaded-glass windows and an enclosed porch. A spring-fed lake is just steps away, past two tennis courts and a hot tub. The house sits on 145 acres of pristine Sussex County woodlands in a naturist resort. It is priced very attractively at $395,000. Still, it has languished on the market for more than a year, even as its price has been reduced from $450,000. How can such a home defy the roaring real estate market in...