Despite a somewhat encouraging second quarter, national online brokerage ZipRealty posted a 20 percent drop in revenue and a $5.1 million net loss in its third-quarter earnings report released Tuesday.In response to the decline, ZipRealty announced a transition of all of its agents into independent contractors among its strategies to strengthen the company -- the change will be effective as of Jan. 31, 2011. ZipRealty operates in 35 markets in 22 states and Washington, D.C. About 2,000 of the brokerage's 3,305 agents are currently employees and will be impacted by the change to an independent contractor model. ZipRealty's California agents became independent contractors on Sept. 1 and the company's Las Vegas and New York agents are also independent contractors."We believe this ...