Some additional thoughts on merchant adventuring in Traveller. Whether it is classic novels like the Polesotechnic League and Chanur series, games like Merchant of Venus & Rogue Trader, or tv shows like Firefly, it is a pretty popular trope and should be right in Traveller's wheelhouse. And Traveller traditionally acts like it is. But in practice they have always treated it as a sort of default situation that everyone knows how to run. So additional material on how to do star mercs, how to do Lt. Leary/Honor Harrington, how to do pirates, etc gets published. But trading is pretty neglected.
Merchant Prince and GURPS Far Trader are pretty high level background with little or no practical how to actually run a campaign at the PCs and their ship level. And this is a question that I"ve seen hundreds of times in the 40+ years I've been running Traveller. So it is not nearly as obvious as it has been treated.
And when you look at the very few adventures published related directly to merchant adventuring,.... Leviathan and Skandersvik both have the PCs as crew on someone else's large merchant cruiser. The adventures make sure the players have local autonomy, but they aren't actually in charge and the NPCs are primarily responsible for the actual trade related stuff.
Which leaves us with The Traveller Adventure. It is a pretty good sourcebook, despite the first two adventures being problematic. But even there, you are putting the the PCs in a situation that doesn't arise naturally from character creation. They are crew of a fat trader with a subsidy in place. A subsidy that turns into a patron situation later on when a major NPC buys out their contract. The structure of the subsidy (prior to the patron buyout) is pretty interesting, but it doesn't flow out of anything that would normally happen creating characters.
The thing is that Traveller is a game about adventurers. And if you look at the fiction like Chanur and Firefly, that's about people who are nominally merchants getting into pretty traditional adventures with the merchanting being the hook, not the main activity. What Traveller desperately needs, imho, is a how to run merchant campaigns product line that:
1) Offers a variety of ways for the players to finance their ship: subsidies, break even handwavium, space trucker, speculation and smuggling, etc
2) Rules and advice on how to do all of the above in a way that is FUN and puts the focus on how that turns into adventures.
3) Example adventures and mini campaigns (like TTA) that actually acknowledge that the PCs are merchants who get into trouble, not freelancers for hire who happen to have their own transport. The latter is a fine campaign style, but it is a different one.
4) Includes some stuff on how to integrate some merchant stuff when the PCs' main ship is non a merchant ship (lab ship, safari ship, yacht) that isn't just "roll on some tables".
5) Different types of trading campaigns: free traders, trade pioneering (mixing merchanting with exploring), building a trade "empire", etc
Traveller's current support for merchanting is basically just some tables to roll on. Tables that generally are pretty easy to turn into excessive profits. What it lacks is advice on how the referee uses those tables to generate adventures and how to introduce trade related complications like competition, corruption, unexpected expenses, and all the things that keep those profits in line IRL. Without the ref seeming like a killjoy who is stomping on the poor players who are just using the rules as written.
Sorry about the wall of text. But, as I said, this is a topic that I've seen brought up hundreds of times. And I'd really love to have answers besides "buy some stuff for other rules like Suns of Gold."