Their ethics direct giving more than a fair value for the price, which is never open to negotiation. They have some obscure relationship to Starseeds, but the price for this information is too high.
Outsiders are estimated to be the most advanced species in Known Space, possibly the Galaxy, but the extent of their development remains unknown. Though they have the technology to produce advanced faster-than-light drives, they rarely use them, preferring to travel the "slow" way. They do possess a "reactionless drive" technology that allows them to reach this speed almost instantaneously. Louis Wu says that the Outsiders have "something better" than hyperdrive.
They spend all of their time following Starseeds and acting as information brokers to space-faring sentient races throughout the Milky Way. Their prices can be very high and scaled to the estimated impact the information will have on the civilization of the client race. Their most common wares are interstellar propulsion systems of various types. The Outsiders maintain a strict commercial ethos regarding any form of knowledge, which shrouds them in a secrecy only wealth can penetrate. They do not haggle. Questions about themselves have been priced on the order of a trillion credits.
They are many-limbed beings that are invariably described as a cat o'nine tails with a fattened handle. Their body composition includes ultra-cold superfluid helium. They live on thermoelectricity by lying with their heads in sunlight and their tails in shadow; the temperature difference sets up a current.
The Outsiders are thought to have evolved on a cold world with no atmosphere.
For thousands of centuries they maintained a trading relationship with Puppeteers and are the source of most of their technology. They are responsible for revealing the hyperdrive technology to Humans and thereafter maintain a trading base on Neptune's smaller moon, Nereid.
The novel A Darker Geometry by Gregory Benford and Mark O. Martin revealed that the Outsiders were created by a race of extra-dimensional aliens seeking to escape the heat death of their own universe. Larry Niven's own writings have neither confirmed nor denied it, however, he has stated personally that it is not canon.
The Outsiders may have inspired the Melnorme, from Star Control 2, another highly advanced and very mysterious species. The Investor species in Shaper/Mechanist stories by Bruce Sterling have a similar ethos but an altogether different biology.