The current system is absolutely ridiculous, boring and confusing.
=> First of all, the character with the higher charisma should define the prices for everyone...
No one would care that it wouldn't "always make sense" (very limited number of situations) but it would be a GREAT QoL improvement (less items management, less confusing, easier to understand,...)
Furiousgreg's argument "what would be the point of having a high CHR and Bartering Skill" doesn't make sense at all => There aren't any Bartering skill and having a high charisma is always usefull for a few classes and for other skills (Deception, Intimidation, Performance, Persuasion). A lot of pain and eventually a lot of mistakes for bad reasons.
=> Second, as OP said, and I totally agree... We even don't see any proficiencies for other characters which is extremely confusing because, in a normal person's head when you click on another portrait the active character is the one you've just clicked on.
But well... not in BG3. In BG3 you have to cancel the trade, select another character and talk again... Impressive ! Just threw that system in the bin and let us really select another character in the trading menu rather than giving us another 3D model for the sake of nothing.
=> Third : rather than this small and orange "not proficient with this weapon" in the tooltip... seriously just add a red layer upon the item icons or a border or "idk what" so we don't have to look all tooltips over and over again with every characters to see if they're proficient with them or not...
You select Gale and directly see what he can (not) use, then you select Shadowheart and directly see what she can (not) use and so on... Something that's not really like that, but it will give you an idea if you haven't played much other cRPGs in the last 20 years.
The trading system reminds me of another poorly designed system that Larian took from their previous games without even trying to improve it to current cRPG standards.
(you know, the chain system).