Accurately estimating property tax

[Eric Lee]

Hi fellow BPers,

I'm new to real estate investing, and am looking into SFHs as rental properties in the Dallas area.  I'm trying to improve my methods for estimating expenses when analyzing deals, and I had a few questions related to property tax.

For example, when I look at a property on Zillow, I might see figures like this:

Why does Zillow show the property tax as the same each of the past 3 years, if the assessment value has risen?

In the MLS listing for this same property, it lists "Unexempt Taxes" as $3,173.

From the county website, I know tax in this area is 2.82%.  For this property I see an appraisal value of 148k, so the estimated 2017 tax is listed as $4174.

In general what is the method that you find the most reliable for estimating property tax?  I assume it would be the county website, but sometimes I can't find a recent appraisal value to use, so knowing the tax rate doesn't help.  In other cases I can see past years tax filings, but the owners sometimes have exemptions that won't apply for me, so I'm not sure how to factor that in.

Appreciate any advice you have to offer!