You may remember when real estate listings firm Zillow first burst on the scene back in 2006. While there are many online real estate listings sites, Zillow distinguished itself with its “Zestimates,” an algorithmically-derived valuation for every house in the United States. Many Americans amused themselves throughout 2006 checking Zestimates for their own homes, as well as the homes of neighbors and friends.

Zestimates were never intended to be appraisals. After all, Zillow has no idea what is on the inside of any home. But the Zestimate algorithm does use many of the same approaches as appraisers use, including comparisons of recent sale prices of similar houses and historical sales trends. To the average consumer, they sure looked and felt like appraisals, and in a sense, that’s what really matters.

While Zestimates were unquestionably a brilliant way to launch a new website in a crowded vertical (Zillow become one of the highest traffic websites virtually overnight), Zestimates have always been an awkward fit with the Zillow business model. That’s because Zillow is an advertising-based business.

Think about it from the perspective of the real estate agent – the advertising buyer. The agent is attracted by Zillow’s huge traffic numbers and pays for an enhanced listing to get even more prominence. But Zillow automatically (and prominently) displays its Zestimate right near the asking price. Imagine asking $1 million for a home when the seemingly authoritative Zestimate pronounces the value of the home to be $700,000. As an agent, you’re not going to be happy.

Zillow’s stance is basically, “hey, it’s just an objective data point.” But advertisers don’t want to hear it. And that’s the essence of several recent lawsuits. In one lawsuit, the plaintiff argues that Zillow damaged her selling prospects by posting a lower Zestimate near her asking price and doing so without her permission. Another lawsuit goes further, saying that Zillow agreed with certain real estate agents to “de-emphasize” (read: hide) the Zestimate within the listing, meaning that some agents were getting a more attractive listing presentation, and those that didn’t pay an advertising fee were being disadvantaged.

This may sound like a problem peculiar to Zillow but it’s not. Yelp has dealt with a similar issue for years. In short, Yelp is finding it hard to sell advertising to customers whose listings are chock full of negative reviews. Yelp has been repeatedly accused of “de-emphasizing” (read: hiding) these negative reviews to satisfy advertisers.

The simple lesson here is that objective data and advertising don’t always mix, and that creates complexity and legal exposure unless you are aware of the issue and identify a solution that works for everybody. Those solutions can be hard to find.