As a recently retired realtor, Trulia and other real estate website estimates are not wrong. You need to know how they are calculated. Real estate websites like Zillow, Trulia, etc. rely heavily on public information provided by counties across the U.S. This means public information includes: square footage, lot size, age of home, number of bedrooms, bathrooms, property taxes paid, past sale amounts and dates, etc.
What is NOT included? Layout of the home, condition of the home, any upgrades or renovations or lack of, neighborhood and school district information, style of home (ranch, colonial, craftsman, etc.) and whether homes recently sold are in the same neighborhood or not.
Therefore, if you are selling by owner, you need to do what realtors across the country are forced to do. Explain to buyers that online estimates are useless and worthless because it does not take into account ____. Therefore, the value you give your home to set an asking price is based on (recent homes that have sold in your neighborhood are similar to yours + homes currently under contract).
Hope this helps.