And seeing the result, that guy was a liar.
That drug was not Jet at all, but something odd...
After taking two pills, the person fell to the ground, unconscious.
It was apparent it wasn't Jet, Jet wouldn't make a person unconscious after two pills. When he remembered this evil merchant was selling this to them, the soldiers were furious. They confiscated all the crystals from the guy's body before throwing him outside of the camp's gate.
The small crystals were distributed among the soldiers. However, with the 530 crystals Jiang Chen paid, they were too scared to take it. Thus as the captain, after deliberating for a while, he personally sent the crystals to Jiang Chen and reported the incident to him.
From the moment he saw him, Jiang Chen knew that guy was up to no good, so he was not surprised at all by the report. Jiang Chen paid for that drug purely because he wanted to waste some time and tease the liar.