The tax assessor staff uses their own data to build their case. You can hire an appraiser for an market analysis and usually he has to be present at a municipal hearing. It can be expensive. Some recommend a Realtor for a market analysis but this usually gets shot down at the hearing since little back up material is presented and itemized adjustments are not focused on as points of contention. My experience is that the Realtor is looked at as a second class professional when it comes to trusting his valuation opinion.

The cost effective method is to do your own appeal. When you win your property tax appeal you get a reduction in valuation from the board of equalization and get your tax bill adjusted or get a refund of taxes previously paid.

Overall property taxes seem to be increasing  while property values are decreasing and unless the local municipal government and state government economize, taxes will simply increase. Unless there emerge a groundswell of public protest and spending caps on the ballot, spend and tax are the operable engine. Unless there is a percentage cap on spending at every level of government, it’s like giving your teenage son or daughter a credit card and letting them do with it as they will.