Please please please stop looking at the Zillow estimates, especially when researching Greenwich CT Real Estate. Zillow is a great site if you want to find out what your neighbors house probably* traded for, what it is currently listed for or for a view of their plot, but it is a HORRIBLE site for valuations. This is a computer program based on the west coast that is pulling info from the internet to value homes.
* - Zillow pulls their info from town websites and links which are many many times incorrectly imputed.
For those of you who like data at how wrong it often is take a look at some articles: