Farming mastery, trading mastery and barter mastery have no affect on gameplay.
Barter mastery is fixed to 0 at all times which makes it clear it does nothing. Farming and trading mastery increase with lifeskill gear though even though it does nothing,
I suggest that farming and trading mastery should be fixed to 0 to make it clearer they do nothing (like barter mastery).
That or they could actually try to fix them to do something.
I hope that's not asking for much....