Agree mostly...
Either way, there is some really good posts in this thread.
Excellent write ups, but I'm pretty sure it states that the base line Imperial Standard is actually 7. Of course, it has been months since I read that section so I may have to refresh the memory and see...Props to Ackehece for that comprehensive set of notes on Trade! I'd like to add a little bit to one of the items he calls out:
Cultural differences cannot be understated. I think this extension on the UWP is one of the most useful for those what-am-I-going-to-do-with-these-players moments.
Homogeneity -- How similar are members of the population? High homogeneity can work in your favor as a trader ("Everyone has one! Don't be left out!") or against, ("Everyone already has those. No sale.") Low homogeneity is a good indicator that your potential market on a given planet may be much smaller than the Economic Extension may indicate. It can indicate a planet of niche markets -- can absorb only so many goods of a particular type.
Acceptance -- This one is pretty straightforward. Do they get along with strangers? No? Then they're probably not buying. Or maybe they'll just try and take it from you.
Symbols -- After much pondering on what a "symbol" is and how symbology might manifest itself in a culture or race, this one practically needs it's own book. However, for shorthand purposes, I've taken this to be an amalgamation of art, body language, signage, and architecture -- essentially the visual presentation of the culture on a scale from austere to ostentatious to over-the-top. The higher the Symbols score, the more visually fantastic a given culture may be. That said, using Symbols for RP/Trade purposes can be as simple as, "Can you recognize and read the signs directing traders to the market?" or as subtle as a negative DM on trade negotiations because the trader/broker fails to pick up on the body language subtleties of the dominant culture. Or if you want to go the Jack Vance route, you could have the locals react badly (or pleasingly!) to the characters manner of address or their clothing. "Only actors and vomit collectors wear yellow caps!"
Strangeness -- The farther the number from Zero, the farther this culture deviates from Imperial norms. The farther this number is from zero, the more difficult time you're going to have trading with that culture. And it may not be from lack of desire on the part of both parties, but simply an inability to negotiate. This could be a language barrier, or they could just be too weird to trade with. Maybe it takes a month-long ritual followed by a human sacrifice before they can accept goods from offworld traders. Maybe they want to have a feast and invite the characters to chop off a toe in solidarity with the revelers and throw it into the stew pot so that they all may share in the delights of each other's company before exchanging goods. I love strangeness.
Good luck, fellow Traveller!
Either way, there is some really good posts in this thread.