National brokerage company ZipRealty announced Thursday that all of its agents in California will become independent contractors. ZipRealty has 910 agents in California, about 28 percent of its total number of agents nationwide. As of Sept. 1, ZipRealty will engage all of its agents in California as independent contractors.In all but two of the 35 markets ZipRealty covers, the company's agents are employees. The other two markets are Las Vegas and New York, where agents are independent contractors. ZipRealty was the nation's fifth-largest brokerage by transaction sides in 2009, according to Real Trends. "Given that California is home to the highest percentage of real estate transactional volume within the real estate industry overall as well as for ZipRealty, the need to be flexi...