Czerka is portrayed as being ruthless, greedy, amoral, unscrupulous, and downright criminal at times, doing whatever - in every sense of the word - it takes to make a profit. They are shown to be involved in various criminal activities, including murder, slaving (as seen in the first KOTOR game), extortion, and smuggling, among other things. They are also depicted as being close allies and suppliers of the Sith Empire.
Knights of the Old Republic
In Knights of the Old Republic, Czerka is running a slaving operation on the planet Kashyyyk, made possible by a traitorous Wookiee chieftain named Chuundar (the brother of Zaalbar, companion of the amnesiac Revan) Czerka do not hide that they have great contempt for the Wookiees. However, the Wookiees, with the aid of an exile named Freyyr (Zaalbar and Chuundar's father) and Revan and his companions, lead a revolt against Chuundar and Czerka that ultimately proves successful in driving the company off the planet.
Czerka also had a foothold on Tatooine, experimenting with the native dewbacks to breed "war dewbacks" that were larger and more aggressive than their easily domesticated cousins. They also frequently came in conflict with the local Tusken Raiders.
Knights of the Old Republic II - The Sith Lords
Czerka have integrated themselves into the reconstruction efforts on Telos IV, exploiting the native population to gain access to their natural resources as well as leftover war materials. Czerka did business with the Exchange in order to maintain their control over Telos IV.
The native Ithorians sought aid from Meetra Surik, the Jedi Exile, in regaining control of the project from Czerka and undoing the harm they've done. Together, they are able to expose Czerka's crimes
The Old Republic
Czerka still have a sizable presence on Tatooine. They are responsible for uncovering the mind prison of the Rakata known as The Imprisoned One, who uses nanotechnology to enslave the people of Tatooine (including most of the Czerka employees who found the prison) and turn them into mindless drones.
A Czerka senior executive named Horell vacationed on Nal Hutta, where he hunted the native Evocii for sport.
One of Czerka's research facilities was located on a moon in the Unknown Regions called CZ-198, where many types of bioweapons were developed.
Czerka is still around by the time of the rise of the Galactic Empire, having an exclusive contract with them. Shortly after the New Republic took its place, Czerka discontinued their work with the Empire, showing that they perhaps were not as amoral as they had been in their earlier years.