Boards want proof
An assessment appeal is a factual argument to a board that hears hundreds of them. "My taxes are too high" is not evidence. "Here is what this building earns, here is what comparable buildings are assessed at and sold for, and here is the error in the county's record" is evidence. The whole discipline of a good appeal is assembling the second kind of case.
Here are the categories that carry weight for commercial property, roughly in the order a board tends to care about them.
1. The county's own record for your property
Every appeal starts with the property record card the county keeps on your building: square footage, year built, construction class, land area, use. Errors here are common and powerful, because they corrupt everything the county's model computed downstream. A building carried at the wrong square footage or the wrong class is mis-assessed by arithmetic, not by opinion.
The flip side deserves stating plainly: if the record understates your property, the review process can surface that too, and in our states a board can raise a value as well as lower it. Reading the record before filing, not after, is how you avoid an unpleasant surprise.
2. Income and expenses, for leased property
For income-producing property, appraisers and boards lean on the income approach: what does the building actually earn, and what would a buyer pay for that income stream? The documents that speak to it are the rent roll, actual collected income, actual operating expenses, and vacancy. The county's model assumed market-typical numbers for all of these. Where your actuals are genuinely worse, sustained vacancy, rents signed below the model's assumption, unusual expense burdens, the gap between the model and reality is the case.
Capitalization rates matter here too. The value conclusion depends on what return buyers in your market currently require, and county models can lag a moving market in both directions.
For owner-occupied property with no lease income, the income approach recedes and comparable sales carry more of the load.
3. Comparable assessments and comparable sales
What are genuinely similar properties assessed at, and what have they sold for? Both questions use the county's own data and public records, which is part of why they persuade: the argument reads the county's numbers back to it.
The word genuinely is doing work in that sentence. A board discounts comparables quickly when the properties differ in use, size, class, age, or location. Fewer, tighter comparables beat a long list of loose ones. Some states also recognize uniformity arguments, that your property is assessed above the level of similar properties regardless of market value, but the strength of that argument varies by state and it rarely stands alone.
4. Condition and functional problems
Deferred maintenance, structural issues, environmental constraints, and functional obsolescence, a layout the market no longer wants, all reduce what a buyer would pay, and mass appraisal models rarely capture them. This category needs documentation: photographs, contractor estimates, engineering reports. A board weighs a repair estimate; it discounts an adjective.
What generally does not work
A few arguments come up constantly and carry little weight: the tax bill went up too fast, the owner cannot afford the increase, a neighboring owner pays less without any analysis of why, or an online estimate says the property is worth less. Boards are valuing the property, not the hardship, and they know the difference between a data point and an anecdote.
The work is the assembly
None of these categories is exotic. The counties publish most of the underlying data. What decides cases is the assembly: pulling the record, the comparables, and the income picture together into a number a board can adopt, and then presenting it through the county's own process, including the negotiation with the assessor's office where most reductions actually happen and, when needed, the hearing itself.
That assembly is the work we do. If you want to know whether your building's evidence supports a case this year, start a free analysis. We check the county's own records, and if the value is already in line, we tell you and nothing gets filed.
State-specific process details live in the California, Georgia, and Florida guides.