Located closest to the system's sun, Canceron is mostly a barren, hellish pit. The majority of its surface isn't fit for anything. The entire middle was nothing more than a cracked up desert broken up by volcanoes. The Colonial Fleet used this region for flight exercises - bombing and strafing like there was no tomorrow. Hard for people to complain about blowing up useless land. Also meant that the military was close at hand in case the bad half of the population got out of line.
Canceron is home to two groups, one at each pole.
The Southers were dour folk who mostly lived in climate controlled subterranean mazes. They were good at selling things. Had to be. When your world only had one export and half of it was automatically sent to the other worlds, you get mighty good at making money off the rest.
The Northers were the troublemakers. At any given time, over 2000 federal prisoners toiled in mines digging tylium. Canceron wasn't the system's only prison. Several high-security penal station were located on other planets or moons, but inmates always had the option to transfer to Canceron. In exchange for enduring the hellhole and mining tylium for their home colonies, inmates earned 'reedom points towards early release.
Everyone made out. Except the Cancerons, but that's what happens when you're sitting on the majority of a natural resource the government deems "essential to the health of the colonies."
Canceron is where the black market got started. The Canceron penal colony housed all the really motivated inmates, the criminals with vision. On the inside they planned. When they got out they acted. Some say the head of the black market in the Galactica's fleet, a soft-spoken fella by the name of Phelan, spent some time on Canceron. That would explain all his connections, it also explains his less-than-sunny disposition towards the military.