What evidence a board actually accepts
Public records beat opinions. Four good comparables beat twenty weak ones.
The most common reason a residential appeal fails is not that the argument was wrong. It is that the evidence did not support the argument that was made.
The hierarchy
Roughly in order of how much weight it carries.
| Evidence | Weight | When it applies |
|---|---|---|
| The subject property's own recent arm's-length sale | Highest | You bought or sold recently |
| A professional appraisal at the correct valuation date | High | Any market-value argument |
| Documentary proof of a factual error | High | Record is wrong |
| Assessment comparables (uniformity) | Good | Uniformity argument |
| Recent sales of similar properties | Good | Market-value argument |
| Photographs of condition | Supporting | Alongside another ground |
| Contractor estimates for repairs | Supporting | Condition arguments |
| Zillow or similar automated estimates | None | Never |
| Your opinion of value | None | Never |
Why your own sale outranks everything
Every other argument reasons from what similar properties are worth. Your own recent sale is what a real buyer actually paid for this property, at arm's length, on a recorded deed. A board that will argue about comparables all afternoon has very little to say to a closing statement.
The Cook County record bears this out. The decision reason "this is the result of a sale analysis of your property" appears on 38,821 decisions and resulted in a reduction in 100% of them. The mirror image — "this is due to an analysis of the sale of the property" — appears on 41,856 and resulted in a reduction in none. Your sale is decisive in whichever direction it points.
What "arm's length" means, and why it matters
A sale between family members, a foreclosure, a short sale, an estate sale, or a transfer into a trust is not evidence of market value. If the assessor is using such a sale against you, establishing that it was not arm's length is a real and winnable argument.
The uniformity evidence that actually works
For each comparable, give the board everything it needs to check you without doing work:
- PIN and address
- Class code
- Building floor area
- Improvement assessed value — not the total
- The per-square-foot figure, calculated
- Year built
Then your own property, in the same format, and the median of the comparables as the value you are requesting. Presented as a table, on one page.
Four or five tight comparables beat twenty loose ones. A single obviously unsuitable comparable gives the office something to reject, and rejecting one is often treated as reason to doubt the rest.
What does not work, and why
Automated online estimates. They are not appraisals, their methodology is not disclosed, and no board treats them as evidence.
Asking prices. A listing is what someone hopes to get. Only completed sales count.
Your tax bill compared with a friend's. Different districts, different rates. This shows nothing about assessment.
Affordability. Genuinely not a ground. Hardship relief exists in some jurisdictions but it is a different application to a different office.
"The assessment went up too much." A large increase is not itself evidence of error — in a reassessment year it may simply be several years of market movement arriving at once.
The one-page test
Before filing, ask whether a stranger reading only your submission could verify your claim in two minutes without looking anything up. If they would have to go and find the floor areas, or work out the per-square-foot figures, or guess which value you are asking for, the submission is not finished.