Traders mainly exist in a fourth dimension and their looks because of that varies from time to time. No one knows where they are from, if they have a homeplanet or anything about their society, if they have a society.
They show up to trade with other races of the galaxy and are known to be very honest traders. Ofte they act in bizarre and strange ways and nothing is really understood about their technology. They take no part in galactic politics. They trade with anything.
Source: GURPS Aliens