Truthfully most interstellar trading games use trade as a way to explain how someone can go from a nobody to a famous space pirate or galactic hero. However, Firefly is technically about interstellar trade as a way of throwing the characters into the side stories. Some of the stories are specifically about shipping cargo, some arn't. I don't see it as impossible but it will either become a backstory with the player's real goals in the foreground or the industry has to be nearly lawless so that backstabbing and various troublemaking is all part of the industry.
I think if you had a tractor trailer driver from the US as a way of developing source material for plot hooks it would make it easier to keep the story on trade. Seriously those guys have weird and wild stories to tell and it's all about hauling cargo.