I'm a L.O. and the other day for example, we had a borrower in Lehi and his appraisal came in 30k less than his most recent tax assessment. In SL County they are a bit more accurate, but not perfect, in N. Utah Cnty there have been too many forclosures and short sales and their assessments are way off...

Zillow usually sucks, usually comes in on the high side, but I have seen it be pretty accurate before. That said, it over estimates value more times than not.