Forbidden practices include using a phony house number, since stars' home addresses are well known to celebrity watchers. Even though the property is not in his name, Pierce Brosnan's 13,000-square-foot Malibu beach megalith showed up for lease this summer at $250,000 a month with zero as the street number. Jennifer Aniston's agent put her trust-held place in Beverly Hills on the MLS with a zero street number when it first came on the market last year at $42 million.
Other tactics — such as labeling the assessor's parcel number as "unavailable" or posting a photograph of a flower, a sleeping puppy or other unrelated subject instead of the house image — are also against listing service policies about accuracy.
"The most valuable asset of the MLS," Ives said, "is the integrity of the data."
Sometimes an agent will withdraw a listing or allow it to expire to hide a sale because the agent has signed a confidentially agreement with the seller. To combat that tactic, the MLS combs through housing data, cross-references and enters any missing closings and prices.
"I sympathize for the agents who have signed a confidentiality [agreement], but it's a double-edged sword," Ives said. "Now that everything is all over the Internet, it's really public information."