A federal jury ruled on Tuesday that the powerful National Association of Realtors and several large brokerages had conspired to artificially inflate the commissions paid to real estate agents, a decision that could radically alter the home-buying process in the United States. The realtors’ group and brokerages were ordered to pay damages of nearly $1.8b. The verdict allows the court to issue treble damages, which means they could swell to more than $5b.