A skill could indeed provide a civil ability aura. You'd have to apply the appropriate aura for the ability level, which would require some scripting. The kind of scripting you'd do would be something like:
EVENT
VARS
INT:_Barter
STATUS:_BarterStatus
ON
OnSkillCast(__Me,"Shout_BarterShare")
ACTIONS
IF "c1&c2"
CharacterGetStat(_Barter,__Me,Barter)
IsGreaterThen(_Barter,0) // Yes, then, not than :P
THEN
Add(_Barter,-1) // index of GetElement starts at 0
GetElement(_BarterStatus,_Barter,"Barter1Share","Barter2Share","Barter3Share","Barter4Share","Barter5Share")
CharacterApplyStatus(__Me,_BarterStatus,-1,1)
ENDIF
This script basically checks the caster's barter skill, and then if it's greater than 0, it gets the appropriate status through GetElement. GetElement picks the status, using _Barter as an index. GetElement starts the index at 0, meaning an index of 0 = Barter1Share, 1 = Bart2Share. Hence the need to subtract 1 from _Barter.
You'd place this event in the Player.charScript or Base.charScript and create a skill named BarterShare which wouldn't really do anything in itself. I'm probably using GetElement slightly wrong, so don't expect that to work perfectly as I posted it.
Then you'd create 10 different statuses, 5 Barter Auras, and 5 +Barter statuses that these barter auras provide.
It would all be a bit clunky, but could work. You'd have to cast the barter skill every time you get an additional barter point, but it'd be permanent otherwise.
There are probably other, better ways to go about this as well, but not positive.
I'm going to release a reworked lucky charm sometime in the future which makes lucky charm provide additional loot from combat, removing the aspect of +loot from objects, making the need for a designated looter moot.
You can see what's available for char scripts in this thread:
http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=605357#Post605357