But some buyers just freeload. (The Internet has a way of encouraging this behavior.) They can search the M.L.S. for a house with no brokerage firm listed, meaning it's being sold by the owner, and then work out a no-commission deal directly with that owner. So you can see where this is headed. If agents want to protect their commissions, they have to restrict access to the M.L.S. to sellers who are working with them, not going it alone.

Local realty groups have tried suing agents or brokerage firms that put "for sale by owner" listings in the M.L.S., accusing them of copyright infringement. Those agents have countersued, charging restraint of trade. Then two years ago, the Realtors association found what it thought was a better solution. It passed rules that essentially allowed a local M.L.S. service to block access to the listing service to any brokerage firm who discounted commissions or who posted listings for homeowners who intended to sell their own houses. The antitrust division of the Justice Department cried foul. This month it sued the Realtors' trade group, asserting that the rules stifled competition and hurt consumers.

The Realtors changed the rules just as the federal case was filed. But J. Bruce McDonald, deputy assistant attorney general, said that the group's policies continued to discriminate against innovative brokers and "stifle competition at the expense of home buyers and sellers."

In a news release, the Realtors association said it was "at a loss to understand" the Justice Department's legal action. "Many of the changes incorporated in the new policy are in direct response to concerns they have raised over the course of the two-year investigation," it said.

The Justice Department and the Federal Trade Commission have successfully fought state real estate boards that tried to limit consumer choices by imposing service requirements or forbidding commission rebates, but the fight goes on. Realtors have lobbied for and won state laws that prohibit commission rebates to buyers and require minimum levels of service, like requiring that an agent handle all negotiations or house showings. Federal regulators can't fight that.

Aaron Farmer, a discount real estate broker in Austin, Tex., has battled local and state realty boards to offer cheaper services. The Justice Department and the F.T.C. intervened to help him. Nevertheless, he has had to raise his fees to $700 from $600 because of the minimum service levels required by a law recently passed by the Texas Legislature. (Eight states have enacted such laws, accepting the real estate industry's argument that they are needed to protect consumers.) "All of these fights are over the M.L.S.," he said. "They don't want price wars."

But price wars are coming. No doubt about that. Here are a few suggestions on how to take advantage of the changing environment to sell your home with minimum services from -- and fees to -- a broker:

Set the price Being a nosy neighbor is still the best way to know the market. Walk though every open house and find out later what the house sold for.