For several reasons I wiped and reinstalled Arcanum and restarted. One of the reasons was the inability to install the recently discovered Extra Animations. Not being a veteran Arcanum player, I doubt I will suddenly notice 'hey, that is new and improved', but I just like the idea of having the best possible gaming experience - which all the excellent mods are providing, the HiRes mod is especially and immediately noticeable. However, after the reinstall I was surprised and pleased to notice that now improvements in Skills actually result in improved performance. This was immediately noticeable with Haggle when I raised it to L2 I saw an actual decrease in Merchant prices, unlike previously where there was no change at all. The fact that my spells are more effective could just be because my PC is now a pure magic user, but Haggle is independent of that and clearly behaving differently. I guess the lesson to be learned is be careful to install in the right order.
Mind you, bartering prices are also determined by how the shopkeeper reacts to you, e.g. beautiful people sell things dearer and buy things cheaper.
I suspect that is also part of the situation. I have changed from guy with a scar and mixed magic and tech, to a pure magic user with no scar and I'm seeing a huge drop in prices for the same level of Haggle (from 1143 to 750) and a seeming increase in spell effectiveness. I think I've replaced a bad setup for one that fits much better with the game's parameters-which is much more fun to play.
Well whatever it might be, it definitely is working more nicely and after you sacrifice the black roosters, they make fine fried chicken.