CHA was giving Wyll better prices in my playthrough.
Also, you can raise the "attitude" of NPC's just like in Divinity. You can do this through various means, but the easiest is just gifting them some items. The investment will net you a vendor to dump all your goods too for better prices.
Not saying I am in love with this, just explaining the mechanics to you.
I also had different prices based on who I was using for my vendor interaction. Shadowheart had the highest Charisma out of all my toons, so I used her for the sales. In fact, I didn't sell anything for a long, long time. I figured I would gain favor with the vendors by completing some quests first, and they would potentially give me better prices. That didn't seem to have much effect, but using a toon with a better CHA sure did the trick. I would guess it's somewhere in the neighborhood of 15-25% savings.