Washington, DC - March, 3: Renata Ko, with her husband Jeremy and son Sebastian, used real estate web sites to conduct research when hunting for their new home. (Bill O'Leary/WASHINGTON POST)

Whether you’re searching for a home, preparing to sell or just nosy about your neighbors, real estate Web sites include so many new features that they can become addictive.

Instead of waiting for an agent to dole out listings on their time schedule, you can search anonymously at midnight, receive e-mail alerts about newly listed homes or open houses, see market and neighborhood reports, map recent home-sale prices, and use apps that display listing details and interior photos of nearby homes.

Nearly 90 percent of home buyers used the Internet in their house searches in 2011, according to the National Association of Realtors. And even if you aren’t looking for a house, it’s easy to get sucked into these sites for their voyeuristic appeal — you just can’t help yourself from peeping into your neighbors’ listings and sales history, seeing their estimated home value (and competitively comparing it with your own), and getting a glimpse into their homes and finances. Admit it — you’ve peeked.

But house hunters, sellers and real estate agents say the quality of information can vary greatly from site to site, and tension is brewing between third-party syndication sites — such as Zillow, Trulia and Realtor.com — and traditional real estate brokers and agents. Brokers have complained that some of the information on these Web sites can be inaccurate or misleading. They say that outdated listings leave buyers frustrated when homes they thought were available are actually sold, and they can leave sellers angry when price reductions aren’t reported quickly.

What is the biggest gripe by agents and brokers? They complain that their own for-sale listings are being used as lead-generating tools for other agents, who pay the Web sites for advertising space or buy a percentage of the inquiries related to when a user looks at a home in a specific Zip code.

“Everybody looked at the Web as a great marketing tool, so they pushed everything out without thinking about the integrity of the information,” says Hoby Hanna, president of Howard Hanna Real Estate, who does business in Pennsylvania, Ohio, New York and West Virginia.

Hanna considered removing his firm’s 35,000 annual listings from all of the third-party sites. But the eyeballs were too valuable to give up: More than 30 million people visited Zillow in January.

No major Washington-area brokers have pulled their listings from the big Web sites, but a small number across the country have done so. Still, knowing about the behind-the-scenes battles can help you figure out how to make the most of these sites while avoiding some of the problems.

Marc Alberts and Kimberly Dinh developed a Web strategy for their home search through trial and error.

The couple started looking for homes after their daughter, Olivia, was born eight months ago – when they were ready to trade in their Shirlington Village rental in Arlington County for more space and an easier commute in southeastern Fairfax County. They started their search at Trulia, Zillow and Realtor.com, which made it easy to find out about neighborhoods and school districts. But the listings weren’t always up to date.

“There were a couple of houses that we found online early on and were really excited about, but then we’d drive by and it would have a sale pending sign in the yard,” Alberts says.

They ended up using a combination of sites for their research. Redfin was Alberts’s favorite site for listings. “They accurately listed open houses and seemed to update any change in status quickly,” he says.

Then they’d go to Trulia, Zillow and Realtor.com for more information on the homes and the locations. They used Realtor.com for its mobile app on Alberts’s smartphone, especially while checking out neighborhoods during the weekend. And they’d use Zillow primarily for its Zestimate — an addictive feature that estimates the value of your house based on public records, similar sales in your area and other information (See box for more information about each of the sites).

As they got closer to making a decision, they worked with a local agent to visit the houses, learn about the market and complete the deal. “People are having to see fewer homes because they’ve done their initial research on the Internet,” says their agent, Brian Block, managing broker for RE/MAX Allegiance in Arlington. “It can really help you narrow down your search.”

In mid-February, Alberts and Dinh bought a 3,300-square-foot home in Kingstowne, with plenty of room for Olivia to crawl. They paid less than $600,000 — and were happy that the Zestimate was about $38,000 higher than the asking price.

Where does the information come from? Zillow, Trulia and Realtor.com are third-party syndication sites — which means that they aren’t agents or brokers — and they get their listings from a variety of sources.

Trulia, for example, has more than 1,000 data providers. The information comes directly from the local multiple-listing services in many areas (there are more than 900 in the United States) and also from brokers, agents and other listing syndicators.

Most of the listing information on the third-party sites for the Washington area comes from one source: Metropolitan Regional Information Systems. It is one of the largest multiple-listing services in the United States and covers all of Maryland and the District, Virginia down to Richmond, and the Eastern panhandle of West Virginia. When agents put up homes for sale, they put the listings on listing service. Most brokers in the area have MRIS send its listings directly to the third-party Web sites, but some choose to send the listings themselves, and a few opt out, says David Charron, chief executive of MRIS.

MRIS also makes its basic listing information available to consumers at its bare-bones Web site, HomesDatabase.com. “Third parties may or may not update their databases as often — we have no control over that,” Charron says. “Some claim it’s every 15 minutes or every day.”

Agents can manage their listings on the third-party sites, even if they don’t pay for advertisements. “There was a time when I didn’t pay attention to it,” says Ken Montville, a RE/MAX United Real Estate agent in Upper Marlboro, Md. “But now I go into all of my listings as soon as they hit Zillow and Trulia, which is usually about two days after I list it on the MLS, and I add some information. I want to make sure that I as the listing agent am associated with the house.”

Montville registered for free with Zillow, so his information will appear with his listings. But since he hasn’t bought any of Zillow’s advertising programs, the names of agents who bought space in a Zip code where his homes for sale are located may also appear. (Agents can pay to have their ad appear a certain percentage of time — such as 25 percent — for someone searching for a home in a particular Zip code.)

He does pay another Web site — Trulia — just under $1,000 per year to ensure that his contact information will appear every time someone searches for a home in the 20740 Zip code through Trulia’s Local Ads program. “It’s not cheap by a long shot,” he says . “I get occasional leads but no solid business.”

He also pays about the same amount to advertise his listings at Realtor.com, which also allows him to add more pictures and details about the homes. He said he will likely continue to advertise on Realtor.com but probably will not continue with Trulia’s program.

Redfin’s listings are updated more frequently because it is actually a brokerage — a Seattle-based Web-based brokerage that also has local agents. It also has direct access to listings services similar to local brokerages. Redfin also includes notes from its agents who have visited the house, reviews of Redfin agents, a popular mobile app and tools to help you do your own market analysis. Redfin identifies the listing brokerage in small type but includes contact information for its own salaried agents, who receive bonuses based on customer-satisfaction ratings, next to the listings.

“Our business has been growing like crazy,” says Glenn Kelman, Redfin’s chief executive. “But it’s easier to get someone to search our site for listings versus to give a Redfin agent a try.”

Renata and Jeremy Ko used HomesDatabase, Redfin and Trulia for their search after their son, Sebastian, was born 18 months ago. They wanted to move from an apartment in Chinatown to a D.C. neighborhood with young families and a good elementary school.

They used the Web sites to learn about the marketplace and neighborhoods, and they ended up focusing on Burleith and Capitol Hill. A friend suggested that they contact agent Gary Jankowski of Coldwell Banker in Capitol Hill. Jankowski gave them listings and alerts that were similar to the listing information they found on the sites.

“When I saw that it was the same information, I figured that if we’re going to work with an agent, we might as well get the listings from him,” Renata Ko says. “We don’t have a lot of free time, and the value of the agent was also to help us negotiate, pull up comparable sales and let us know about houses that aren’t on the market yet.”

The agent also helped with intelligence gathering — knowing whether a house is getting many offers or if the listing agent purposely under prices a home, Renata Ko said.

The Kos recently put a contract on a house near the Capitol that never appeared on any Web site. Their agent found it for them before it went on the market.

Kim Lankford is a freelance writer.