https://wiki.project1999.com/Game_Me...2C_and_Faction
Basically this excerpt from that:
1. Key to this is that, whether your faction is apprehensive or indifferent or better, there's a stretch from 62 to 76 that gives exactly the same prices. So, if you can get your charisma up to 62, don't bother getting any more charisma boosters until you can get enough to get you to 76. However, when you do get to 76, the prices will suddenly drop by about 6%, instead of the 0.5% boost you get for most individual points of charisma.
2. Better known is the "magic number" of charisma, 104. This is the point at which indifferent or better merchants will give you the best price they're ever going to give you. This price seems to be based on 1.05 times a "actual value" that you will never see used, but is only directly known by the server. For instance, many gem and metal prices are clearly based on this. And, if you notice the prices at which the vendor will buy such things back from you, although it looks like a very irregular number, for instance 95pp 2gp 3sp 8cp for a bar of platinum or a sapphire, that just happens to be 100pp divided by 1.05.
3. The last and highest number to shoot for is 132. This is the charisma at which you can normally get the cheapest prices even with apprehensive faction.
You're likely in one of the CHA ranges where changes to faction don't matter.
-Mcoy