The 'official' view of junkers is that we're a group of individuals from every race, culture, and faction around Sirius who have joined together as salvagers for profit. We collect scrap and valuable equipment that's been lost in debris fields or on derelict ships, and we recondition and sell that scrap and equipment for cash to further our operations.
Unofficially, we run the entire Sirius black market with the exception of Kusari space. For the right price, we will acquire for you anything your heart could desire - from the best ships, to the best weapons and equipment; we even work with slaves (gotta love those slave girls), cardamine, and artifacts.
The two big factions we really have to worry about are the corsairs and outcasts. Both of them are extremely valuable allies, but we play a dangerous game trying to be friendly to both. On one front we smuggle cardamine for the outcasts in exchange for access to their space, equipment, and protection. On the other, we smuggle artifacts for the corsairs in exchange for the same things from them. Neither side really likes that we work for the other, but we're valuable enough that they wont hassle us about it.
We also offer 'safe havens' for criminal groups in most of sirius. When they're being hounded by the law, they can stay at our bases and hide. We bribe anyone and everyone to keep them out of our business and off of our stations in order to maintain that privacy.
There are really only two factions that dont like us - xenos and hogosha. The hogosha dont like us because we're foreigners (gaijin) and they want all foreigners out of kusari space. They also run the black market trade in Kusari, and they dont want us taking over in that department.
The Xenos would benefit greatly if they allied with us, but they're stubborn. They want to corner the black market trade in liberty so they can start making some big money, but with us around they cant do that.