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 They say that outdated listings leave buyers frustrated when homes they thought were available are actually sold, and they can leave sellers angry when price reductions aren’t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.