The traditional Traveller-style free-trader game is a fine sandbox, but is sometimes a bit too directionless. Players wander about wondering what to do, and this impairs involvement.
On the other hand I’ve run a lot of mission-based campaigns recently.
On the third hand I keep banging on about the telenovela narrative shape in RPGs.
So how about this? PCs are all people who have some useful “hard” shipboard skills (piloting, navigation, maintenance) and no particular commitments. They, and a second-hand merchant ship that has just been sold by Honest Kaagira’s Used Starships and Oak Furniture (Closing Down Sale), are here. The purchaser of the ship is there, some months’ travel away. (Perhaps it was a knock-down price, or the buyer wants this particular rare model of ship for the job they have in mind.)
So there’s an overall drive: in order to get paid (and more importantly not to have the ship repossessors sent after you), you need to get the ship to there by a particular date, in reasonably good nick. But any money you can make en route you can keep.
The default answer to “what do we do next” is always “carry on towards our destination”, but there’s plenty of scope for working out how we can get into trouble on this planet. The ship may have a history. If the campaign is set in the actual Traveller Imperium, there are horribly-detailed books of worlds to serve as adventure generators. And the game has a defined scope: the red line across the map has a specific end point. (Though, using the TV model, if the ratings are good the trick could be repeated with a different ship on a different journey.)
Traveller has fairly tamperproof ship registration, I believe. One needs something like that for the premise to work – not just in terms of PC-proofing, but because nobody would buy a ship from a remote dealer if they didn’t have a reasonable assurance it would arrive. (Or they’d send a company crew to collect it.)
It appears that you intend to have the PC’s paid by the purchaser upon delivery. One variant you might consider is to have the patron be the seller, instead: perhaps a dealer in luxury yachts or other custom designs, who could afford to hire a crew to make the delivery.
As unique vessels, these ships would be very difficult to conceal or to fence to anyone other than the intended buyer. Since these are shakedown cruises, unexpected maintenance issues are always available as complications. (The patron might provide equipment insurance for major subsystems, so the PC’s aren’t left paying to fix someone else’s vessel, but the shipyards that honor it might be off the direct route.) The ships wouldn’t have to be commercially viable, either, and might have some odd features. The patron could provide minimal operating funds (via letters of credit, say) and bonded return tickets from the delivery world – probably travelling low, to encourage the players to scrape up at least enough funds to upgrade to mid or high. The patron would then pay off the PC’s in person upon their return.
If the campaign is going well, the next ship (with a different set of quirks and peculiarities) is waiting to be taken to a new destination in a different direction. Some runs might be leisurely, some might be under a time constraint. You could control the length of your story arcs by setting the distance to the delivery world.
In Traveller’s Imperium with its distinct tech levels, this is the sort of thing a high-tech world could do: sure, you may live on a mud-hut-and-scurvy hellhole, but if you’ve just robbed the planetary treasury, you’ll be able to afford at least a small yacht.
Which leads to amusing PC-facing problems on delivery too.