Mass Effect: Stardust
These groups are either rarely seen in Citadel Space, or are secretive in their dealings. Depending on the circumstances, they may aid PCs, but such aid is never without a benefit to themselves. While not always openly hostile, PCs should be aware of the unknown nature of their motivations.
It is extremely unlikely that PCs would have any knowledge of the inner workings of these groups, and any Knowledge checks made to determine an individual’s information on the group in question will be extremely difficult. Most (like the Collectors, or Cerberus) are just nearly impossible to even know of, barring extraordinary circumstances; these groups guard their anonymity viciously.