Patricia Quintilian had to convince an assessor that the second floor of her dome house was smaller than the first.

After appellate lawyer Patricia Quintilian built a geodesic dome home on 27 acres in Goshen, Mass. in 2002, she was forced to develop a new specialty: property tax law. For five years in a row, she contends, the local assessor valued her home too high and made such basic mistakes as listing the first and second floors as having equal square footage. "It's a dome," she protests. One year she took the dispute up to the state's appellate tax board, which decided her home was worth only $241,600. The next year the local assessor was back with a new $355,600 valuation. "The property tax system is broken," declares Quintilian.

She's right. Local assessors, sometimes part-timers with little training, too often guesstimate a home's assessed value. That number is then multiplied by the tax rate to determine your annual real estate tax bill. "Do not assume an assessor is necessarily an ‘expert.' Assessors are often elected officials lacking any special skills," warns the National Taxpayers Union (NTU) in a handy guide, How to Fight Property Taxes, downloadable from its website for $9.95.

What makes that bad situation even worse these days is that some state and local governments have raised real estate tax rates to compensate for falling house values and/or weak sales and income tax revenues. So a too-high home assessment becomes even more painful.

Higher tax bills, the greater information available on the Web and the growth of special low-price appeals services are all leading more folks to challenge their assessments.

Is it worth fighting? Peter Sepp, executive vice president of the NTU, estimates that 20% to 40% of those who appeal win some reduction. Billionaire Tom Golisano saved $100,000 last year by appealing the $6 million assessment of his Mendon, N.Y. estate to a state court, which cut the assessment in half. "The New York system is very unfair to taxpayers," says Robert Jacobson, Golisano's attorney.

You're more likely to save hundreds than thousands, but here are nine steps to take when your next tax assessment arrives in the mail.

### 1 Pin down the basics

First, determine the assessment base, which is usually (but not always) stated on the bill or in an accompanying pamphlet. In some localities properties are assessed at a fraction of market value. A too-high assessment representing 80% of your home's value might look reasonable if you wrongly assume it's 100% of the value.

Next, determine the assessment date. Your home's worth as of that date--not its current value--is what's significant. Some areas have three- or five-year revaluation cycles. Your house, now worth $400,000, might show a $500,000 assessment, based on 2007 values. You can still appeal this year's bill, but understand you'll be fighting over what your home was worth back then, not what it is worth now. Even more confusing, some areas phase in multiyear assessments, meaning your annual assesment could--legitimately--be rising, even while your actual property value is falling. You can always appeal a current tax bill assessment, but you usually can't go back and fight over last year's bill.

### 2 Act quickly

Deadlines and rules vary, and most are not taxpayer-friendly. You might have only 25 days after getting your assessment notice to file an appeal and then only a few days until the hearing. Meanwhile, pay your bill on time; an appeal won't ordinarily delay the due date.

### 3 Get your property record

Your assessor's office has filing cabinets (or a computer) stuffed with "tax cards" for each property. "It's a gold mine of information," says Richard Michaud, a real estate lawyer with Bernkopf Goodman in Boston. Even if the assessor has put information on the Web, you'll usually get more details by visiting the assessor's office.

Check that all information is correct, including the square footage, number of bathrooms and fireplaces, and the quality (or depreciation factor) used to value your home. If you find factual mistakes, go in for a friendly chat and ask the assessor to correct it. "Your tax assessor isn't your enemy. He's an official trying to do his job. Often you can work these issues out very informally," says Michaud.

### 4 Be a nosy neighbor

While you're at the assessor's office, get your neighbors' property tax cards if you can. Assessments are always available as public records, and often the cards are, too.

You have a good chance of reducing your tax bill with an appeal if your house is assessed for more than what similar, nearby properties sold for or are assessed for. If all the neighbors have made improvements, and you haven't, make sure your assessment is lower. A drive-by assessor might have judged all the houses as being of equal value, unaware that only yours still has the original lime-green bathroom fixtures, no central air and a wet basement. Think like a buyer trying to talk down the price of your house.

Another resource: The real estate agent who sold you your house might put together a list of comparable property sales (not listings) for you in hopes of a future referral.

### 5 Use the Web

You can search for all the houses on your cul de sac on Zillow.com or Trulia.com and compare basic stats (size, number of baths) and the assessment and sales histories--a particularly useful exercise if your locality hasn't put such data online. Warning: The value estimates on these sites tell you what you might sell your house for today and are irrelevant for your appeal. Boards can throw out the data you submit if it postdates the assessment date.

One new Web service, ValueAppeal, charges $99 (refundable if you don't win) for online help putting together an appeal package, including up to 15 comparable property sales. Before you pay you plug in your address to see if you're one of the 25% of folks who ValueAppeal estimates can save $300 or more a year by appealing. (If not, the service won't take your money, giving it an 80% success rate, claims founder Charles Walsh.)

### 6 Consider hiring a pro

If you're not intimidated by local bureaucrats, you can argue the initial appeal yourself (typically in front of a local board). At the other extreme, if big dollars are at stake or you fight all the way up to court, you'll likely need a lawyer.

In between are various services that file a large number of appeals. Some don't require any payment up front from you; instead they collect a share (usually 50%) of the first year's reduction in taxes. That's not a bad deal if the assessment will affect your bill for three or more years.

Or you could find a local pro who specializes in your area and knows the detailed (and possibly quirky) criteria that affect assessments there. "The system is nuts," says Sheila Anderson, who does appeals in Florida for residential and commercial clients. "If you don't know what's in the pages and pages of criteria that affect how you are assessed, you could be blindsided," she adds.

### 7 Don't shoot yourself in the foot

If the facts don't support your case, an appeal could actually lead to a higher valuation of your property. Perhaps the assessor has listed your lot as larger than it is but missed your addition. Be aware that an appeals board will likely ask what improvements you've made to the property, whether or not you ever filed for a building permit. You'll be under oath when you answer.

### 8 Search out exemptions

You might also get your tax bill reduced by finding an exemption you qualify for and aren't getting, such as a homestead exemption for a principal residence. Also common are exemptions for low-income seniors and veterans. Marc Soss, a tax lawyer in Sarasota, Fla., returned from service in Afghanistan and found he was eligible for a one-time $1,500 combat rebate on his real estate taxes. Separately he filled out an application, as a disabled vet, to get $5,000 chopped off his assessment, translating to $70 a year in savings. "Most people are completely unaware of these breaks," says Soss.

### 9 Work to reform the system

After a partial victory knocking $400 off the annual tax bill on her family's one-story stucco Odessa, Fla. home, Sara Cucchi, a former industrial engineer and now stay-at-home mom, is applying to be on her county's appeals board. "I want the system to work the way it's supposed to work," she says.

Lawyer Quintilian, for her part, wrote a book filled with horror stories and advice. Its title: Are You Getting Screwed on Your Property Taxes?