I can't see a downside to simply allowing the Manifest Scanner to work from SC TBH, and only benefits.
How about it's a tad vague, and depending on your distances and the quantity they have, it may/may not resolve it?
eg:-
So, from a long distance in SC:-
Gold 50t
---- ---
---- ---
You get closer:-
Gold 50t
Silver 10t
---- ---
And not until you interdict and scan:-
Gold 50t
Silver 10t
Some-rare-thing 1t
Note: Too far away and no details would be given at all!
Or a variation where the quantity is always shown, but what it is is determined by distance/quantity?:-
So, from a long distance in SC:-
Gold 50t
---- 10t
---- 1t
You get closer:-
Gold 50t
Silver 10t
---- 1t
And not until you interdict and scan:-
Gold 50t
Silver 10t
Some-rare-thing 1t
I would go a slightly different route on this which still allows a reasonable mechanic and provides a reasoned "probability" of cargo carried by each ship.
Follow me along on this...
Our ships' scanners easily distinguish the hull type and other equipment fitted to each scanned vessel.
Our ships' computers could easily be programmed with data on the approximate mass of each hull type and the likely mass of each module fitted.
The only things a scan does not fully reveal is the actual grade of each module, (and therefore basic unmodified mass of each module), and also any cargo carried
The manifest scanner might only be able to ascertain the overall mass of a vessel whilst in SC.
The upshot is that - IN LORE - a probability estimate could be provided by the computer of an amount of cargo carried. And if you want to go a bit further, an error probability could also be displayed.
Of course, the actual mechanics of equations and functions don't need to programmed into the code, just an approximation could be used.
For vessels far away in SC - the error probability is high and the cargo probability low.
For vessels inside long range FSD Interdictor range - the error probability is medium and the number of tonnes of cargo estimate is provided within certain bounds. For a medium vessel carrying 50T you might receive scan reports such as:
Cargo estimate 20-40T (35% error probability)
For the same vessel inside typical Class 1 Grade D FSD Interdictor range:
Cargo estimate 41-46T (80% error probability)
Something along those lines would be my own suggestion, just to give a rough feel for the probability of cargo being carried, simply because it is pants that the NPCs transmit about juicy cargo when there is no mechanic available to players to rationalise this kind of transmission (other than outside intelligence, of course, like you've been scanned leaving a station and that info has been broadcast to a wing or onto a pirates' information dissemination system for forward transmission to the pirates' network - which again could be a tool that appears in game but only for players who have gained reputation with illegal pirate factions - you know - like *content* for pirates).
I'm not simply against piracy - I think piracy could work in this game - but in the current construct it is so nominally close to zero fun for traders that this is the source of the whining. The beef, largely, is not that piracy exists, but that it has no consequences for a pirate and nothing but consequence for traders. There is no symbiosis. There is no eco-system. Only pain on one side and none on the other. Of course, this is the majority view where on the other hand a few players might actually find being a targeted traded fun...
Cheerz
Mark H