About 11% of home sellers last year used "alternative" brokers (ones offering flat fees or other forms of discounting), up from less than 2% in 2002, according to surveys by Real Trends, a publishing and consulting firm.The competition from discounters has prompted some traditional brokers to use a variety of tactics to fight back, and this can end up hurting consumers. The controversy will get a public airing Monday when the Consumer Federation of America, a nonprofit research and advocacy group, releases a report on "how the real estate brokerage industry functions as a price-setting cartel."