While homeowners are usually delighted to receive high appraisals on their properties, consumer advocacy groups strongly suggest taking a second look at a property’s value before popping the cork on the champagne.

The New York-based public policy group Demos charges that there has been an epidemic of mortgage appraisal fraud that has left home-buyers and refinancers struggling with higher mortgages than home equity, and the possibility of foreclosure. If property values level off or decline, the many homeowners who have been fooled into taking out oversize mortgages may not be able to sell for a high enough price to pay their mortgages off, Demos said in a March report, “Home Insecurity: How Widespread Appraisal Fraud Puts Homeowners at Risk.”

The problem stems from the desire of lenders, brokers, and real estate agents to inflate the value of residential properties to make higher profits, Demos said. To achieve this goal, loan originators have been putting more and more pressure on appraisers to overstate property values.

A former independent appraiser in northern Texas, Bob Burnitt, recently left the profession because he was so frustrated with what he perceived as corruption in the industry. He said loan officers often told him to abandon an appraisal if it did not meet a certain value.

He cited an example involving a regional Bank of America manager.

“She sent me an appraisal request, and it said that if I couldn’t get a value of so many dollars, to call them immediately and stop the appraisal,” Mr. Burnitt said. “When I told her that that was a violation of the rules, she canceled the appraisal right away.”

An appraiser who refuses to adjust estimates does not stand a chance at making a living in the industry, Mr. Burnitt said, because loan officers know there are lots of other appraisers willing to step in and play by their rules.

“When I say I can’t do it because it’s a violation of the law, they always counter with, ‘Well the other appraisers do it, why don’t you?’ “Mr. Burnitt said. “I don’t live my life that way, and that has made me absolutely unemployable.”

Many other appraisers share Mr. Burnitt’s view. Some 8,000 signed a petition to the federal government complaining about pressure from lenders.

When asked what she thought about the issue of mortgage appraisal fraud, a Bank of America mortgage loan officer declined to comment. Bank of New York representatives did not return phone calls.

Loan officers are not the only source of the problem, according to Demos. Homeowners eager to pay off credit card debts and meet rising living expenses are being urged to “treat their home equity like a bottomless ATM,” and to encourage appraisal fraud by pressuring lenders to wrap up deals quickly, cutting out the appraisal step.

“In many cases, homeowners are their own worst enemy,” the author of “Home Insecurity,” David Callahan, said. “Everyone wants the cheap cash to in many cases pay off credit-card debts. And most people who are refinancing their home just want the deal to close. They don’t want any problems. I think that’s really shortsighted.”

Homeowners refinancing their properties often expect a certain appraisal value, Mr. Burnitt said, and stubbornly refuse to accept a lower amount.

“Some homebuyers have an almost adolescent or childlike view of their finances,” Mr. Burnitt said. “In other words, they don’t care what it costs, it’s just, ‘can I get it?’ “

The National Community Reinvestment Coalition, a group that helps consumers who feel they have fallen afoul of predatory lending, says that many of the victims of mortgage appraisal fraud are minorities.