Zillow Inc. and Yahoo have extended into 2014 an exclusive advertising agreement by which Zillow provides for-sale listings to Yahoo Real Estate and sells ads featuring real estate brokers and agents that appear on both sites.Zillow.com and Yahoo Real Estate are two of the most visited real estate listings portals on the Internet. The advertising alliance gives Zillow the ability to sell ads to real estate brokers and agents that appear on both sites, splitting revenue the ads generate with Yahoo.Zillow's annual report suggests the listing and sales partnership generated between $5 million and $10 million in revenue for Yahoo Real Estate last year.Zillow said its cost of revenue increased by $5.6 million last year, to $10.6 million, an increase "primarily attributable ...