A federal jury this week delivered a major blow to the American home-buying industry by finding that the National Association of Realtors and several large brokerages had conspired to keep agent commissions artificially high. The decision, which awarded plaintiffs nearly $1.8 billion in damages, is seen as a game changer and has sparked more antitrust lawsuits against the association and brokerages. Real estate experts predict that changes are coming to the industry, including making commission sharing optional, negotiating for the home seller to cover the buyer’s broker costs, charging flat fees or billing by the hour, and even forgoing buyers’ agents altogether. Analysts estimate that as much as 30 percent of the industry’s commissions could disappear as a result. Start-ups are also trying different business models to adapt to the changing landscape. The brokerage industry could potentially contract, leading to a significant impact on the National Association of Realtors. The group has said it will appeal the court ruling.