A common man is not guilty, but possessing a treasure is his crime.
Jiang Han wanted to disguise himself because he was worried about being targeted. He planned to get some Xuan Stones from the gambling house. Getting too few would be pointless, but getting too many would surely attract attention from the people there.
Is a gambling house something just anyone can open? There must be a major power behind it. If a major power took notice of him, Ling Yunmeng definitely wouldn't be able to protect him.
So getting Xuan Stones was simple, but the tricky part was concealing his identity. He didn't know any disguise techniques, so he had to consult Jiang Lang.