Different sale prices, value, assessment (Property Analysis)

[Jordan Sizelove]

How accurate is Zillow.com as far as it's "Home Value Index" goes? Was looking up the value of the home I currently rent. The Zestimate says $290,662. However, tax assessment says $191,500. Why such a huge gap? It was sold in 1999 for $157k, in 2001 for $265k, and in 2003 for $330k.

Was looking up another property on ziprealty.com. Property is a foreclosure condo, 2b/1b. 903 sg ft. HOA dues $380 per month. It's been on the site for 60 days. Asking price is $66,800. It sold for $150k in 2005. It also says it was sold for $180k in 2005. It was then listed 09/19/14 for $74k, 10/19/14 for $61k, and 10/31/14 for $66k. Still waiting to be sold. Not sure if this appropriate or not, but here is the link to the property (if inappropriate, please remove):

http://www.ziprealty.com/property/2122-PEPPERTREE-...

I'm looking at the different times both houses were  sold and I'm guessing the huge gaps are either from depreciation or appreciation? If so, considering the foreclosure, would that be a good deal for $66,800? Will the value of the property eventually appreciate back to $150k or even $180k?

Starting to look at properties so I can finally do my first deal. All help is greatly appreciated!