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Black market trader is not available in menu "Enter-5", but still can be found in NPC list that opens in details screen and can be contacted remotely. You can sale illegal wares while out of reach of police ships.
All trader prices and inventories are randomized, so if you see 2 traders of same type, they will have different prices. Sometimes you can buy from one and sell to another for profit without leaving platform or station.
Each remote trade add 2500 Cr transport fee.
High reputation with trader faction will give discount on items. Discount for trader can also be achieved as Smalltalk revard.