barter seems not to interfere after 150% in items price.Speech interferes on the number of people needed to create a faction, time before dialog closes and may interfere with some quests.
barter seems not to interfere after 150% in items price.
If you want to make enemies, try to change something.
This should depend on the trader you are using, some of them have Barter skills that would make having 150%+ worthwhile