In credits.
The idea is that if you are caught committing a crime (that isn’t violent) such as running with your transporter off or causing an Extreme level of suspicion on the black market, some factions will demand you to pay a fine.
I think the penalty of losing 1 or 5 relations points for being caught smuggling or having the transporter off be too little, and i find it a bit weird that the law-enforcement aren't fining people.
I think a mechanic for fines would make, at best smuggling harder, or at worst more annoying.
How i imagine this could work, would be something like:
Get multiple fines at the same time:
Say you where caught with the transporter off. That’s one.
They found illegal goods on your cargo, that’s smuggling. That’s another one.
Trading with the transporter on in the black market and causing extreme level of suspicion should grant you a fine on top of losing reputation.
More if a patrol ship decides to stop you after you cause the extreme level of suspicion, and you run away, that should count as another fine, because you run away from authorities.
And if you cant pay when patrols stop you.
You should be able to pay it later on one of the factions stations, say, a time period of 30 days to pay it. If you still don’t pay up, you lose reputation (tho it should only reduce to a certain number as to not make you hostile to the faction) and the fine increases for missing the timeline and a new one starts.
Miss too many times, and the law (as long as you are in the core systems) will come to you and demand that you pay up.
Now there should also be ways to not pay the fines or avoid them even after being caught.
Ways to doge fines could be.
Bribing patrols to look the other way
Becoming hostile to the faction by accepting a commission from a rival factions.
Tho the fines shouldn't simply disappear and once you are no longer commissive and the relations are what they where before the commissions, you still have to pay the fines.
Having certain characters, that could use their influence to forgive your fines in exchange for some credits.
I believe this could also work well with contacts, say having friends in the right stations that tell patrols to ignore you or have no patrols, ignore black market activity, or having patrols friends that during their work shift are willing to ignore you, or pretend to do a scan your cargo.
I think every faction should be able to put fines (except pirates and the luddic path) but it should different from each other, some more tougher than others, some could make you pay for running with your transporter off and having illegal cargo only, others would demand that you pay for the value of the cargo that they confiscated on the system on top of the other fines.