If you're doing For Sale by Owner, you need to understand that many agents pay monthly subscription fees to Trulia, Zillow and other real estate websites. Agents pay the fees to advertise themselves and to gain prospective leads from buyers contacting them. The majority of buyers do their real estate search online, so its only natural that agents advertise online. In return, these websites give the agents advertising space on X number of listings they pay for - including yours. You have no control over this. At this time, Trulia receives listings directly from the MLS & 3rd party websites - but not from For Sale by Owners, so I'm wondering how you posted your listing. For Sale by Owners have to visit a different website that posts to Trulia. Zillow.com allows For Sale by Owners to post directly to Zillow and Zillow now owns Trulia too.
As for comparing your home to others that have nothing in common - understand that both Zillow and Trulia use automated valuation models to create their estimates. The estimates are rarely accurate and is primarily used for marketing purposes for both Trulia and Zillow. The estimates are based on county public records and do NOT include condition of home, neighborhood facts that buyers would take into account, any upgrades or lack of, any exterior additions that are not in county public records and many other factors.