What effect would the feat "Natural charmer" have on bargaining?

[Gravitygroove]

I'm playing an oracle of bones and going to be needing large amounts of onyx soon. I have an 18 Cha, +13 diplo and natural charmer at the moment.

How should that effect trying to get a discounted price for quantities of onyx (or anything really) in the confines of the game rules?

[Bandw2]

it doesn't actually, it just makes it easier to convince someone to accept outlandish offers, and they still won't go below 75% of the price.

the bargaining rules are REALLY weird.

[Gravitygroove]

yeah i couldn't really make any sense of the bargaining rules even having read them twice.

Why can't they simplify into a more elegant system? I guess Natural Charmer is a bit of a wasted feat on my part.