(Washington Post illustration with BigStock and iStock photos)

Jon Coile, chairman of Rockville-based multiple-listing service MRIS, writes occasional commentary on the Washington area housing market.

Whether you are just mildly curious about your neighbor’s house or actively searching for your next home, online real estate viewing has become our national pastime.

According to Comscore, online real estate search sites get more than 100 million unique visitors a month. Considering that there are only about 400,000 home sales a month, it would appear that the majority of those 100 million visitors are not actually active buyers.

[To make it home sweet home, there’s an app for that]

Online listings have made real estate a whole new ballgame. Unlike the old days, when real estate agents relied on newspaper ads that by design only provided partial information about a property, online listings now can tell consumers almost everything they need to know about a home before they even get in to see it.

The counterpoint to all the great information on the Internet, though, is that it’s still a little bit like the “Wild, Wild West” out there. You’re counting on everyone to play nice in the sandbox, but the non-Realtor sites are unregulated. There are Web sites that may look like legitimate For Sale By Owner (FSBO) ads, but they allow anyone to post listings for sale, even for properties they don’t own. You think you’re contacting the actual owner, but you’re really dealing with someone sitting in a cubicle in “the cloud.” You can also be looking at a listing that says “Click here to talk to an agent,” but it’s not necessarily the listing agent, and the person may actually know nothing about that specific property.

[Mobile real estate apps help take guesswork out of house hunting and renovation]

It’s also important to keep in mind that while Google is great for most searches, the one place it fails is real estate. A number of companies game the system to try to attract buyers. They’ve indexed every street address in America and pay to get to the front page of Google search results. If you Google “123 Sycamore Drive,” the first two or three pages of listings are often going to be out-of-date garbage. They might have what appears to be a video tour, but it’s really just a single still photo taken from a legitimate listing.

So, how do you know which of the countless real estate sites on the Internet are worth your time? Here’s a guide to the four best sources, starting from the top, casual voyeurism, and drilling down to the serious buyer who has identified the property they want to buy.

 Zillow.com: Think of Zillow as primarily for entertainment purposes. If you’re just nosing around for fun — you want to see the inside of your boss’s house or want a rough idea of what your in-laws’ home is worth — Zillow is a great place to start. They have what they call a “Zestimate” of the value of all 130 million properties in America. But they are not known for accuracy; which is why they don’t call it a “Zaccurate.” Zillow is also not always reliable in terms of what’s for sale and what’s not. They often show properties as currently listed that are not on the market, and vice versa.

[How accurate is Zillow’s Zestimate? Not very, says one Washington area agent.]

[How accurate is the Zestimate? Zillow says the tool is helpful when used the right way.]

• Realtor.com: If you’re just starting to think you might want to buy, but you don’t yet know if that’s going to be in Annapolis, Indianapolis or Minneapolis, or you’re toying with buying a vacation property in some other part of the country, visiting Realtor.com is a great first step. It’s highly accurate, showing only actual properties that are for sale, and is updated every 15 minutes. You can get a sense of what the market is generally like in a given area, or you can see lots of photos of a specific home.

• Local MLS public facing Web sites: Once you’ve drilled down and you know the area you’re going to be looking in, you need something even more accurate. For that, you want the public Web site for the local MLS (multiple listing service). Three hundred of the 800 multiple listing services in the country have a Web site like this, covering about 80 percent of the real estate market nationwide. You can find it just by Googling for it. The local MLS public Web site — here in Baltimore/Washington it’s MRIShomes.com — will have almost everything that’s available to real estate professionals. You’ll see all the properties for sale in real time. If something sold even a minute ago, the site will reflect that.

• Listing brokers’ Web sites: If you drive by a house you love and want to know more, go directly to the listing broker’s or agent’s Web site. That may have even more information than the MLS site. You’re going right to the horse’s mouth.

[Online real estate sites spur rethinking among traditional brokerages]

It’s also important to remember that a virtual listing is just that: virtual. If you are truly interested in buying a home, the best advice is that once you’ve narrowed down your selection you should get off the Internet, find a licensed agent and visit the homes in person to get a feel for the properties and neighborhoods.

Catch up with some of Coile’s previous columns:

How borrowers can help make the mortgage application process go smoother

It’s not too early to get your home ready for a spring sale

Open houses now attracting Web-savvy clients who actually buy