I have run into a problem where sometimes players (or a team of players) stop trading with others pretty early in the game.
This happens when that team, by chance or by some luck in trading with others, gets a set of rule cards which seem to be well enough to them.
I.e. they know that (sets of) 1 or 2 commodities will give them a nice number of points. So they see no need to trade with others, and keep the rule cards that they have to themselves. Even though there are (or might be) rule cards in the game which would tell them that 1 or 2 of these commodities, will score negative points under certain circumstances.
I would rather not tell players upfront what kinds of rules there are in the set, as I think it is part of the fun of the game to discover this while playing. However, the example above shows that without this knowledge, a team can be content with their rule cards and commodities quite early in the game.
How would you fix this?