Question: Why do real-estate agents and appraisers set prices for homes based on comparable sales in a neighborhood? I think this practice can only reduce the value of a home. I've put $350,000 into my home, but now I'm told it's worth only $200,000.

Vito: There's a good reason why real-estate agents and appraisers use data from recent "comparable" home sales to calculate house prices. Buyers ultimately determine the prices in any real-estate market, not sellers, and comparable- sales numbers provide the most up-to-date way of determining what buyers are paying for similar properties.

That doesn't mean the comparable sales approach is always spot-on. Typically, real-estate agents and appraisers pore through lists of recent, similar transactions in a given neighborhood and then use those prices as a basis for determining what the latest home will sell for. But sometimes, the other recent sales aren't all that comparable. For example, if your house is a modernist masterpiece in a neighborhood filled with 1930s bungalows, it could be a little harder for all parties involved to accurately assess the value of that property.

If you suspect the real-estate agents or appraisers you're working with didn't accurately determine the value of your property, you do have some options. First, you should ask for a full recounting of the agent's or appraiser's work to make sure he or she didn't make any obvious mistakes. If that doesn't work, you can always hunt for another opinion, though doing so could require hiring an appraiser at your own cost. If all of that doesn't help, you could disregard the advice of your agent and try to sell the house on your own, at your own estimated price. If you were right, you might wind up selling the house for a lot more money than you would have gotten otherwise. But be forewarned: If you're wrong, your house could sit on the market for a long time, and that could make it harder to sell the house later -- even after you lower the price -- since some buyers are wary of a property that has been on the market too long.

It's also possible you could run into trouble even if you find someone who's willing to pay a higher price for your house. If the buyer needs a mortgage, his or her lender will likely require an appraisal to make sure the property is worth what the buyer is paying. If that appraisal comes out significantly lower than the price you and the buyer agreed upon, the lender might refuse to make a loan for the full amount. That will, in turn, jeopardize the sale.

Indeed, you do have to remember to be realistic about the situation if there's a dispute over your house's value. If a host of other experts are telling you your house isn't worth as much as you thought, they very well could be right. The job of appraisers and real-estate agents "is to be objective and provide realistic market value," says David Barca, a broker at zipRealty Inc., a low-cost real-estate brokerage based in Emeryville, Calif. "Sometimes, as homeowners, we can overstate our perception of market value because some of the things we appreciate about our property have little or no value to a prospective buyer," he says.

It's also worth remembering that many big-ticket improvements you make to a home don't recoup their full cost. In other words, if you've done a lot of work on your house, you shouldn't be surprised if the total expense of that work doesn't show up in the list price when you decide to sell. That's not the fault of appraisers and real-estate agents. Buyers simply aren't willing to reward a homeowner for the total cost of an upgrade. Homeowners can in many cases expect to recoup only between 60% and 80% of the money they spend on home-improvement projects. You might want to consult with a real-estate agent before making any major upgrades to a home if you're worried about not being able to recoup the expense later on.

Using recent comparable-sales results as a basis for determining a home's value is not a precise science, and it can at times lead to some disappointments for sellers. But it's still the best system for estimating values for assets whose prices are dictated by the marketplace. If you think your home is being undervalued, get a second opinion. But if multiple parties agree that the appraised value is close to accurate, you might want to take that into consideration before opting to put the house up for sale at your own, preferred price.

-- Mr. Barta is a staff reporter for The Asian Wall Street Journal. His "House Talk" column appears every Friday exclusively on RealEstateJournal.com. E-mail him your questions about the residential real-estate market. Please include your first name and city and state. If your question is answered and posted, we will show your first name and city. Due to volume of mail received, we regret that we cannot answer every question.