The correct answer to this open question is the following.
The Qing Dynasty responded to foreign attempts at trade during the
18th century in unfriendly terms because during the Qing Dynasty, China though that they were a superior nation with the power of imposing its will on other territories. Chinese rulers considered that the Empire was superior to other nations in culture, army, and trade. So if other nations wanted to trade with China, they had to accept, first, submission to the Emperor, somehow as vassals to the Chinese ruler. And of course, this was not accepted by some nations who considered it as an aggression.