How much does Charisma effect vendor prices?

[Vanessa]

I know that generally speaking, a higher charisma means merchants will buy your items for more, and sell for less. But I was wondering, how much of a difference does it actually make?

For example, if I have 100 Charisma then sell an item to a vendor for 10pp. Roughly how much more would that same item sell for, if I had 200 Charisma, instead of 100?

Does anyone have any idea?