The agent is responsible for entering correct data in their local MLS.
Aggregate websites can and DO change that data. For instance, the information regarding contacting the most knowledgeable professional regarding that property is REMOVED. In nearly every case, other agents are presented in a fashion easily mistaken by consumers as the listing agent. Some properties, appearing as listings, will show computer generated data in the description field. In others cases data entered by the agent can be replaced by other feed sources. An agent who had a listing a year ago may find this property listed for sale this year. As the question submitter observed, the listing can be completely fabricated!
Maybe you can answer the question regarding which data has precedence, tax records showing a home with 1200 SF or data from the MLS showing 1700 SF? How often then would an agent be required to visit the THOUSANDS of aggregate websites to keep the listing from being overwritten by public data sources? The notion an agent can, even if they desired to, maintain the data integrity over hundreds if not thousands of aggregate websites indicates the expansive reach of this problem is not well understood.
Be aware the questioner posted a question regarding data appearing on Trulia, an aggregate website, not data appearing in the local MLS, where data integrity is monitored and enforced.
As the questioner observed, and as others have repeated many times, data integrity on aggregate websites render them useless and this is due to the ACTION of the these aggregate websites and has NO BEARING on the behavior of the real estate professional. The AGENT DID PROVIDE TIMELY< ACCURATE, RELEVANT, data that was changed, suppressed, overwritten or fabricated by these websites. An agent can choose to set up accounts on the Hundreds of aggregate websites and check them weekly (what about the sites they don't know about?) or they can accept they can not spend time cleaning up the mess created by irresponsible parties and choose to be an educator. "If you are serious about making a real estate decision, you need access to serious resources.?
Agents should be seeking a true alternative to irresponsible aggregate websites, direct consumer to that site and advise sellers not to syndicate to organizations who exhibit no concern for data integrity and has a clear process for hierarchical data importing.
It seems however, that will take too much effort. Too many choose to justify misleading the consumer. There is no excuse for websites fabricating data and no place to hide for those who advocate and benefit from such practices.
Hopefully Barry words, "I don't understand why the words "bait and switch" did not appear in any of the answers, but it's no matter. I'll stick with the words "For Sale By Owner" serves as a wake-up call for those who are asleep at the wheel.
Of course I know Truilia does not support FSBO.......at this time.