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.