Fluffy Bunny Feet
Cosmic Mongoose
They know all the regular buyers/sellers and have them on speed dial and can take them to their favourite restaurants/bars/brothel or whatever and avoid things that annoy them. They also know who needs it NOW and who is just stock piling. They know all the regular ships that "run the route" and can be trusted from those who can't. Outsiders there for a week just don't know those things as it takes years. Then again there may well be a prejudice against Travellers who always seem to be causing trouble, except when they need you of course.I am a little confused by the comment in the rules
"Local brokers gain DM+2 on negotiations, since their local knowledge helps them find the best deal and avoid the pitfalls of dealing with outsiders."
They are like the small town lawyer at home going against the big city import. One of them knows the judge, jury and witnesses the other does not.
Or like the small town politician who goes to Washington as a lobbyist but doesn't know anyone and doesn't know WHO to lobby due to the power they hold behind the scenes that an outsider wouldn't know. You just waste your time and money.