Trade: Brokers

I'm curious how the presence of broker (potentially also their willingness to work with you) is determined, RAW (rules-as-written), if it exists as a written rule. Also I'm curious how it is determined in this game, of course. Edit, currently my assumption is that it's 0,0,1,2,3,4 on a d6, but I have no idea and I wasn't able to find an answer in the 1977 or 1981 version of the books.

Brokers are NPCs.  I look at the population of a world to give me an idea of the quantity of brokers which then suggests a quality.  Quartermark and Mensah are population worlds with high tech levels so they both experience a tremendous amount of trade, which means all quality of brokers can be found.  Therefore I don't make a big deal out of allowing top of the line Brokers to be hired on either planet.  You might remember that the players have started giving their business to a new Broker on Quartermark.  One they helped establish and have a positive relationship with. And like every business a broker wants to make money so if you have something for sale most will help you for a fee.