Here is how I look at it whenever I scoop up some slave canisters, and deliver it to a "Black Market", to "sell"; I am not selling those poor enslaved people trapped in a tin can back to slaveholders, but rather to a Federal Station Black Market- where slaves can be freed by an "underground railroad" fence operation.
So imagine the Black Market at Chango Dock; a shady, illegal district somewhere in that station. Hidden among the drug dens and assault weapon stores, there is a "liberation front" sort of place, where a pilot can deliver severely illegal cargo such as Slaves secretly and out of sight of the strict Federal law and officers. The slave "purchaser" pays the pilot for the slaves- not as a payment of goods, but rather as a reward for freeing them!
Slaves cannot be handled in the direct commodities market, and thus, in full legal view and jurisdiction, a canister of Slaves would be trapped and confiscated, and probably returned to the original "owners" as returned stolen property, per strict and blind stolen property laws and regulations.
So, the liberation front has to be "illegal" and undercover, and may very well be funded and manned by secret agents of the Fed, but nevertheless has to do things secretly to not set off the soulless bureaucracy of trade customs and laws and international alliances and agreements.
So its tricky. The slaves must be delivered to a black market front, cracked open (strictly speaking; looted after being stolen), and the liberated people given false ID's and shuttled off to a world in federal space that is in need of colonist and workers looking for a "new life". The credits that are payed out for smuggling them there (and for paying your delivery reward) may come from special agencies, rich charity organizations (discreetly funded by guilty feeling slaveholders in the Empire that actually have a soul), or Black Ops funds and budgets, that again; has to remain outside of Federal law and eyes (plausible deniability is king here)
So, be the "hero" to those poor slaves you encounter drifting in space. By all means: scoop them up gently, and take them directly to a federal black market (not an anarchy one, no NO!). Get paid the reward for delivering them to their new life, and fly off into the sunset with peace of mind and glowing satisfaction.
(And remember: Denial is just a river in ancient Egypt.

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(And Delusion is a De-illusion, meaning its TRUE!

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[the above two reminders mean you must trust that the slaves are freed, and not just making up a story such as this to simply sleep better after making a hefty profit from it all

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