"...the fact that they offer market-value estimates and 'are promoted as a tool for potential buyers to use in assessing [the] market value of a given property,' shows that they meet the definition of an appraisal under state law. Not only should Zillow be licensed to perform appraisals before offering such estimates"
It can be surprising when seemingly innocuous activities are in fact heavily regulated (cf. Stanford needing to remove all their learning videos from their website).