They weren't real merchants. No real merchant would behave like that. They were just pawns the "eastern merchants" tried to use to force Rimuru's hand. Considering who their master is, I reckon they might have just failed their mission and forfeited their reward, whatever it might be. I wonder if they even get to keep the dwarven gold they just received. The mafia might take all of that back. That's How Mafia Works.