This is a dangerous question, because trading in general has nothing to do with killing. The trade is an ancient form of exchanging goods between people, for instance, a farmer could exchange his crops to some coins or another goods.
The trading was a reason of discovering new countries and continents ages ago. The trade as an economic term has lots of ebbs and flows, but it depends on the season and year.
Hafiza, this statement is not about trade and killing as general phenomena. Rahter, "no trade no killing" refers to the prohibition of the trade of goods made from endangered animals as a strategy to prevent the killing of said animals. The idea is that rather than focusing efforts on catching poachers, endangered animals would be better protected if that effort was shifted to preventing the sale of goods derived therefrom.