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I'd prefer to leave this until v4 becomes live, but ATM (other than the obvious buy low, sell high - & get your trades in first), smalltalking multiple NPCs to gain stackable discounts can work effectively. if a little tedious.
Each successfull trade improve reputation with station owner faction. Gained reputation proportional to transaction value. You need to trade goods with cumulative worth about 6 000 000 000 Cr to gain 30 relation with faction.
Personal trading via Skunk
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