Logically speaking, if you want to impersonate someone from an organization, it's best to pose as the most inconspicuous person, as this greatly reduces the chances of being discovered.
So when Uncle Li Dong told Qing Chen, "I need you to stir the waters," the young man naturally assumed that everyone was being serious, sincere, and proper at the time.
Qing Chen believed that the person his master wanted him to impersonate would certainly be chosen based on this principle, and then a corresponding character would be selected from inside Spade.
But he never expected that his master wasn't sincere at all.
Nor was he proper.
Who the hell would impersonate the boss of another's organization just for kicks?!
What's key is that when Uncle Li Dong, Lin Xiaoxiao, and Ye Wan showed him the video of Xu Linsen, their expressions were so calm.
Even the thick-browed Mother Ye started to swindle people with a poker face?!