The first thing to realize is that appraisal values can vary, depending upon whether the appraisal is being done for a re-finance or a resale. They can also vary somewhat from appraiser to appraiser. In other words, the work that goes into an appraisal is part 'art' and part 'science' and the standards and efforts vary from appraiser to appraiser.
It could be useful for you to have a Realtor check the comparable values in your area, to make a separate assessment.
Finally, if you believe that your property has been assessed too high a value by the local government, for tax purposes, there is typically a way to contest the amount of tax -- to file a request to have it reviewed. There are many people in the U.S. who are having success in getting their property taxes reduced, on that basis.
Best regards, Eric