Purchase CASS (Coding Accuracy Support System) certified mailing lists.  

@Meghan Chomut The perceived accuracy of appraisals don't really last long.  

I've found that I get 1 out of 25 numbers are incorrect, which is roughly 90% accuracy rate on a 1000-lead list.

The accuracy is very poor in rural areas due to the wide geography.

To be as specific as possible in submitting my OPRA request I was hoping for a few helpful pointers to ensure accuracy.

So I'm getting maybe ~80% of the accuracy of what I could paying a GC to walk the property but I'm getting it free and (most importantly) before I buy a plane ticket to come out.  

On a side note, I respectfully disagree with @Sherman Ragland comment in regards to the accuracy of the responses in this website: "You'll get responses on this website, just the wrong ones."

He owes $42,606 in taxes for 2010 and $38,157 in taxes for 2011 - PLUS a 20% accuracy-related penalty for both years.BOTTOM LINE: The fine tax pros visiting this forum frequently exhort the members/REIs here to keep good records. 

So much for accuracy Zillow. 

Some of the higher volume marketers on BP might be able to chime in on the percentage of accuracy for list provider data, but I would bet it varies quite a bit from county to county.