Well I meant make an aura that gives your allies barter, but the aura itself doesn't give the character that already has barter more barter. But a more simple (and less restrictive) way to do it would be to just have a group buff skill that applies a "dummy" status that doesn't do anything in itself, but is used to check for Barter.
EVENT
VARS
INT:_Barter
CHARACTER:_Source
STATUS:_BarterStatus
ON
OnCharacterStatusApplied(__Me,BARTERCHECK)
ACTIONS
IF "c1&c2&c3"
CharacterGetStatusSourceCharacter(__Me,BARTERCHECK,_Source)
CharacterGetStat(_Barter,_Source,Barter)
IsGreaterThen(_Barter,0)
THEN
Add(_Barter,-1) // index of GetElement starts at 0
GetElement(_BarterStatus,_Barter,"Barter1","Barter2","Barter3","Barter4","Barter5")
CharacterApplyStatus(__Me,_BarterStatus,-1,1)
ENDIF
