I just got to the city after the beach and have found that when I mouse over NPCs with my rogue PC who has 1 barter they have 0 attitude but when I try with my wizard PC who has no barter and the same Charisma as my rogue it shows 10 attitude. My wizard has +2 reputation from the trait that gave my rogue +1 barter. Does this account for the attitude difference?
What is the effect of a 10 attitude difference? I know the +1 barter is supposed to give me 10% better prices than my wizard.
Charisma, reputation and bartering skill are all part of the attitude equation but there is one less visible part as well. Talents like stench can reduce attitude significantly. Maybe your rogue has a talent the vendors don't like.