I've appealed one successfully and have 4 appeals outstanding at the moment.
Our county does the reassessment about every 7 years. The last time I did it I checked the property tax records to see the current and past assessments of the other houses on my street.
Assessments on homes changed in value from about 23% to 56%. One empty lot went up 900% in value. I pointed out that, for a 7 house street in which no house was more than 500 feet from all the others, that was a ludicrously inconsistent rate of increase between the houses.
What's more, the more desirable properties (not next to the loud and busy highway) went up the least.
I pointed out that the house next to ours, which had shot up in value, had sold for 60% of its assessed value just 2 years prior, and that it had been purchased by a contractor who pumped $50k to $60k of improvements into the property.
I noted that not only had my own home NOT had that kind of improvement, the property records showed features (like a deck) that my property did not have.
The assessment had gone up about $60k (50%) and I shaved about $25k off that with the appeal. Not as much as I wanted but still saved me money for the last 7 years.
The 4 appeals I have going now are as follows:
1) We attempted to have our house put up for sale last fall and had received an estimate of the likely sales price from our realtor. It was significantly less than the assessed value. Probably our weakest appeal.
2) Our new house was refinanced last winter and we had to have an appraisal. The appraised value was significantly below the assessed value. In addition, the appraisal is in line with the fact the home was on the market for some years at the assessed value and didn't sell.
3) Rental #3 is not habitable. It was bought at 1/3 of after-repair-value, but the repairs have not yet been made. The house is not habitable. The kitchen is not functional and the floors are torn apart. We argue that it's worth 40% of assessed value until the repairs are completed.
4) Flip #1 was bought last winter. It was abandoned (even by squatters). It is not habitable. The electrical, water, gas, and hvac systems are vandalized and/or inoperative. The roof was failing. All interior ceilings, sheetrock and insulation have to be removed and replaced. Plus other damage.
We maintain it's worth what we paid for it ($101k), not the $354k they have assessed it at.
We pointed out that it had failed to sell for several years at less than the assessed value. We also pointed out that the empty lot next door has also failed to sell for some years for less than the assessed land value portion of the lot.
We also used Zillow to find other distressed properties as comps, arguing that well-maintained properties in good neighborhood are not comparable sales to a property in such a distressed condition. We were able to show that other properties with much less damage had a very steep drop in value.
We'll see. But all told, we're talking about $400k difference in valuations over the 4 properties. We did not dispute our other 2 properties as their valuation was spot on.