Haggling in RPGs

I'm pretty sure I've never seen an RPG implement haggling as a rule. I've certainly done some in-character haggling with NPCs, but never used a game mechanism. Well, I'm on an OSR kick at the moment so I started wondering how I might implement haggling within that framework.

First thought was to use a stat bonus. INT and CHR which both seem obvious choices possibilities. But then there's WIS too. CHR is all about influencing people, INT is problem solving and memory, and WIS is... well, what is WIS all about. Actual IRL WIS would seem to feed into the haggling process but does it apply in-game? In the end I've decided  to use CHR as that just feels more applicable.

For a core mechanism I feel like DieRoll+Mods >= ShopKeep and I'd like to have various levels of shop keeper.

Assuming a roll of 2D8 + CHR mod

Street vendor    9+

Market stall    10+

Shop keep    11+

Artisan    12+

And I like a variable level of success. 

Beat score gets you 30% off. 

Beat score by 2+ and you get 50% off.

Roll snake eyes and price goes up 10%

There you go a first attempt at a haggling mechanism. Please post in the comments any suggested changes!

There you go, my first cut at haggling. I can see you using this in Basic Fantasy or Scarlet Heroes, or even Fallen Justice. To be honest, any OSR title could use this. Especially for starting poor characters.