A ganzu, or revenge society, was a group of Orions that committed acts of vengeance for pay.
A person who lacked the means to exact revenge on those who had wronged them could hire a ganzu to carry out a suitable act of retribution on their behalf. For example, the offense could be a bad business deal or a stolen girlfriend, or it could be some more serious crime with no proof to convict a known perpetrator, or the law otherwise protected them. The revenge could be as simple as a sabotaged grav car to something as involved as looting a warehouse that the victim owned. The cost was usually high, but the results were often worth the price.
Some people who acquired lots of enemies could pay off the local ganzu so that they wouldn't target them. Particularly notorious ganzu could make a good living off this trade alone.
Though they were technically illegal on Orion worlds, ganzu tended to arise wherever Orions lived in great numbers. Members were not professional criminals, but ordinary people interested in dispensing homegrown justice and earning a little extra money, with some added danger and fun. (FASA RPG - The Orions module: Book of Common Knowledge)