I have been appealing property tax assessments for ten years now. One thing I am sure of about a property tax appeal is you never know what you are going to get. Market value is in the eye of the beholder, and every beholder has an opinion. 

An appraisal is an opinion of value. Hire two licensed appraisers to value your real estate and they will both inspect your property inside and out. They will scour the market for the most recent, comparable sales. They will agonize over the reconciliation of the data to select the most likely price you property will bring in the open market. You will most likely get two different value opinions.