Caveat venditor

The housing market slump, rather than abating soon as many "experts" believed would happen, has now reached record proportions. Within this grim figure lurks another problem: half of all houses on the market are now vacant while owners carry two or more mortgages, one on the new house they bought and the other on the old house that remains unsold. This is a looming mortgage default disaster.

The number of vacant homes for sale nationally jumped more than 30 percent in the third quarter from a year earlier, to 1.9 million homes, the latest data available from the U.S. Census Bureau show. That's about half of all single-family homes on the market, said Michael Carliner, vice president of economics for the National Association of Home Builders.

"The share of vacant for-sale is unusually high, compared to anytime in history, really," Carliner said. "Over the past few years, total housing production has been beyond what the underlying fundamentals would indicate."

In fact, the housing slump is now so severe, with so many vacant houses for sale, a new industry has sprouted: contractors who specialize in maintaining empty homes while on the market. Such is testimony to entrepreneurial spirit.