1. The current mechanic is that you you can bribe merchants to change their view of you (and get better prices) by giving them gold -- tons of gold at high difficulty and high levels. This doesn't make a lot of sense, and turns out to rarely be a good deal anyway. (Especially since it sometimes seems to get reset -- maybe on area change?)
2. Instead, please make it based on actual events -- does the character personally like you (and "you" should be main character only -- see point 3), have you done things to help them or their faction, etc. (It seems like maybe this was the intent, but never implemented?)
3. Also, making prices depend on the charisma of whichever character started the conversation is.... just kind of tedious. I feel a little obligated to swap in Wyll every time. Since every player is likely to have at least ONE high-cha party member, this is not really functional. I suggest just removing this entirely.