And then, I'm afraid, we get to the real elephant in the room.
The bartender.
Seriously, I really want someone at Frontier to tell us what they expect us to do with the current implementation of the carrier bartender. I'm at a loss as to what possible use it could be.
It's obviously designed as an on-foot analogue of the commodity trading. So the first question should be "does that work well?".
I'm not convinced it does.
Quite apart from the sheer clunkiness of setting each commodity up individually, the commodity trader can only be of use if commodities can be bought low somewhere where there's high supply, moved somewhere else where there's high demand and sold again for a higher price. The only real circumstances in which this is likely to happen that I can think of in the current game are 1) community goals and 2) mining.
Because there are no permanent NPC ships carrying out economic activities à la X3, this requires other players to be motivated to do it. They have to find it a better use of their time to sell to your carrier (or buy from your carrier at the other end) than to make the delivery themselves. Unless there's some really dedicated miner/trader players out there with no jump range on their ships or no ability to either outrun or outfight any pirates, this seems a bit unlikely.
And, of course, this requires them to know your carrier is even there in the first place. Third party tools aside, there is of course no facility in game to do this other than squeeze in some sort of advertisement instead of a proper carrier name. So unless they happen to be looking around and see you, it's not going to happen. (My first suggestion for this is that carriers be given the ability to regularly broadcast a user defined message in system chat, kind of like NPC chatter).
This aside, however bad the system is, does it translate to the bartender?
No. Bartender resources are not commodities.
They're not produced by the BGS, they're not consumed by it. Beyond player engineering, they have no intersection with any economic activity at all.
As far as I can see no player is ever going to sell a resource to a carrier bartender for less than they'd get for selling it to a station bar. And no carrier owner is ever going to set their bartender to buy something for more than a station bar would pay just to sell it off for the lower price later.
In terms of perhaps setting a bartender up to just buy materials you need for engineering, perhaps that would make more sense - but again, you run into the problem of advertising it. How are other players meant to find out that your bartender is buying these things?
The whole system needs a complete rethink. I would like to see the trading system plugged into the economic system somehow - maybe you could park your carrier in a system that produces goods and pay a fee or premium of some kind for NPCs to transfer the goods over, or to unload at the other end. (I'm not suggesting actual NPC ships doing this, although that would be nice. Handwaving it on board over time would be acceptable.)