Elder Li kept urging Jiang Chen to stay, but the latter stomped out of the Resplendent Emerald Veranda in a thundering rage. He didn't give Elder Li the opportunity to stop him. Jiang Chen hadn't really planned on selling anything to the Veranda anyways. His ultimate goal was to see Wei Xing'er. Since he'd achieved his goal, he no longer had a reason to stay.
He had given Wei Xing'er the powder, but there was a possibility that the stubborn girl might not consume it for fear of putting Jiang Chen in harm's way. Because of that, Jiang Chen had resorted to a few other tricks to track Wei Xing'er.
The Veranda master was a respected figure in the Great Scarlet Mid Regions, but not even Emperor Peerless could see through Jiang Chen's methods, let alone a sixth level emperor. The Veranda master likely didn't expect that anyone would leave an imprint on Wei Xing'er's body. Thus, he'd never considered this possibility and taken any precautions.