The Den just has the one creepy Trade Authority though. Maybe the guy in the bar if you have foodstuffs to sell. I’ve spent too much real-world time waiting 48 game hours in the chairs by the airlock for him to reset. Kind of a drag.
The Key has 8 vendors all with generous cred limits right next to eachother. I think the next best place is Neon, you can run down the central concourse selling to every shop along the way. Assuming you get any “special acquisition” goods past the scanners that is.
::: spoiler I actually assumed that the UC would set up shop on the Key. It was their station originally, after all. If I had realized the vendors would be gone for good, I may not have finished the Crimson Fleet storyline so early. :::