I don't think they do. I think they only provide the Assessed value, which is good. There is no way a national data program can accurately predict a home's value. There are too many variables and local influences. Similar to the military always needing the man on the ground.
The best way to get a value is still through an Appraisal or a CMA. Even what I call a "Blind CMA" is better than what you can find on-line. For this I just use the available public data, any information the owner can give and my knowledge of the area. Before i give a value, I make sure they understand that it cannot be accurate without the property being viewed.
Hope this helps.... more