I will be the first to throw appraisers under the bus for low appraisals, we all know that it does happen from time to time. In their defense however, an appraisal is more complicated than looking at recent solds on Trulia. I would recommend that you request a copy of the report and take a look at the comps that the appraiser used. If you feel you have better comparables you might point them out to the appraiser. I do wish you luck however because as a group I have found that they don't like anyone to question their authority.
#1 Trulia Agent in Minnesota