Home sellers and real estate agents have a new worst enemy: inaccurate home value appraisals.

Even as prices begin to stabilize and buyers re-enter the market, the appraisals many banks rely on to approve financing are causing some deals to fall apart at the last minute, or forcing sellers to agree to lower prices.

Lawrence Yun, National Association of Realtors chief economist, said the appraisal problem is serious.

“Lenders are using appraisers who might not be familiar with a neighborhood, or who compare traditional homes with distressed and discounted sales,” he said. “In the past month, stories of appraisal problems have been snowballing from across the country with many contracts falling through at the last moment.”

The potential problem inaccurate valuations pose to sales can be seen in numbers that measure pending sales of existing homes. Those represent contracts that are signed, but sales that haven’t closed, and are usually considered a more forward-looking gauge of housing sales.

Earlier this month, the Realtors group reported pending home sales in April were up for the third straight month, advancing 6.7 percent from March, with pending sales up more than 3 percent from a year ago. By contrast, closed sales of existing homes in May were up 2.4 percent and remained nearly 4 percent below year ago levels.

The NAR’s Yun said sees a danger of a delayed housing market recovery and a further rise in foreclosures “if appraisal problems are not quickly corrected.”

Still, many indicators continue to point to stabilization in housing.