The current state of on-foot material trading and selling needs to be scraped, it's silly to assume all bartenders are "illegal traders" and the only reason they are was to justify their existence as no other option or feature has been developed for bartenders.
Instead I suggest that a whole illegal trade mechanic be created and it wouldn't be difficult. What I propose is that instead of using the bartender, a randomly generated NPC located randomly in the station is instead designated as an illegal trader. This is not immediately obvious until you approach the NPC (no above head label). When you approach the NPC and press E to interact you are presented an option to prove you're not a member of Omnipol or station security by using a passphrase, this passphrase is spoken by two NPCs chatting to one another in the bar meaning you need to eavesdrop on their discussion. The mechanic would work similarly to asking for higher payment from NPCs for missions, if you pick the wrong passphrase you're locked from illegal trading from that station for possibly a number of hours.
All this could easily be implemented with current mechanics.
