Free online real estate estimates, such as the Zestimates provided by Zillow.com, are a boon to many home buyers. They provide fast, hassle-free estimates of homes all over, with the intention of giving shoppers an idea of what's available before they even head out to look in person. According to the Wall Street Journal, however, Zillow isn't quite as reliable as it seems to be, given the fact that it gives prices down to the dollar, not just round-number estimates. For instance, it listed a 7,600-sq. ft. home in Fall City, WA at $661,756, but the home sold in January for over $2.5 million. The Northbrook, Il. house pictured was pegged at $450,000, but sold for nearly double. And the errors can go the other way, as well, with an El Cerrito, CA house selling for $80,000, though its estimate was over $500,000.

Zillow tries to keep things as accurate as possible, of course, but the bottom line is that it is best to take their estimates with more than a grain of salt just in case the 5% error you are expecting turns out to be 50%.