Like many real estate teams, we post our listings on a variety of third-party websites, some of which are free (CraigsList), others of which we have paid for (
BoiseHomeSites.com or
Homethinking, for example). Until recently we did so glibly unaware of any problems.
We are now a little more informed, a lot less pleased and are doing what we should have done in the beginning: posting a disclaimer in our listing packets about third-party websites.
Here are a few of the problems we've run into.
(a) Listings are sometimes duplicated,
(b) frequently display incorrect or insufficient information, or
(c) are being attributed to agents other than the listing agent.
Zillow is one of the worst offenders, albeit inadvertently. Though it may offer some buyers a real service, it also does them a disservice. Zillow maintains a database of properties in most major real estate markets. They gather data on properties from county assesor records and make it available on their website, regardless of whether or not that property is for sale.

Unfortunately tax records are all over the map (at least in the Boise area). For example, we have a listing that received permits to remodel and expand, substantially increasing the square footage. The assessor's office doesn't show it--so Zillow doesn't display it. While we've corrected the information, Zillow displays the Assessor's information AND ours, which is terribly confusing and, in my judgement, may raise questions about the agent's credibility.
(On the plus side, you can brand homes in the Zillow database as being for sale.)
Google Base is another headache. (By the way, have you tried searching for property on this site? It's a bear. The listings are all but impossible to navigate and the site is cumbersome. If I were I buyer, I'd leave that site faster than you could say, "Does *everyone* have to be in the real estate listing business?!")
Our broker syndicates our listings to Google Base...but that doesn't mean that dozens of other offices aren't entering our listings, too! For whatever reason, some other dude's submission usually trumps ours. That means our clients' listings are branded to any number of other agents, whose tactics are harder to observe and regulate. (This is different from IDX, where, in Idaho, a third-party vendor is necessary for displaying other agents' listings. Those third party vendors enter into a contractual relationship with the MLS and violations, like failing to acknowledge which brokerage holds the listing, are more easily recognized and reported.)
While Google acknowledges that they receive listing submissions from multiple sites (and even provide an inconspicuous link to "All Sources"), the inherent concern remains: Listings may be branded to other agents (not unusual in the industry, but elsewhere dependent upon a mutual arrangement), but violations are harder to identify and report. (Try it: I dare you.)
This says nothing about the fun yo

u'll have trying to explain this to your seller when they visit Google Base to find their listing and validate their relationship with you, only to find it listed (accurately or otherwise) as another agent's.
Homescape and
IdahoHomeSpot are a couple of other third-party sites that we've wrangled with. Of the sites where our listings are syndicated,
Trulia has been remarkably accurate and easy to use.
Needless to say, it’s impossible to keep up with all the online real estate listing websites and what they’re doing. Here are a few suggestions about what we CAN do: