The reason why the Third Patriarch of the Zhang family wanted to know what that person had bought and sold was to get a general idea of their background. After all, the goods a person buys and sells often reflect their social status.
Take martial arts as an example. A martial artist at the Gui Zhen realm is unlikely to buy martial arts at the Yellow or Lower Xuan realms. They would also rarely purchase martial arts at the Upper Xuan or Supreme Xuan realms.
Similarly, a martial artist below the Gui Zhen realm wouldn't buy martial arts above the Di realm, as they wouldn't be able to master them even if they acquired them.
However, with Mr. Han's objection, they were at a loss as to what to do.
Although Zhang Jiancheng didn't possess great wisdom, he was quite clever. His eyes flickered as he said, "Then we can simply buy the same items that that person sold to your esteemed institution, or purchased from it. That shouldn't be a problem, right?"
