Does Barter work the same way in Fallouts 1 and 2? Does anybody have an idea of the mathematical formula from which the sale price of an item derives, and if so, can its generalities be expressed in layman's terms?
Is there a degree of proficiency in Barter at which one reliably can buy at the same price they sell? I noticed prices vary considerably on the same item in both 1 and 2, even outside instances where the price and haggling are based on dialogue instead of assumed on the Barter table, but I'm pretty curious how this is determined.

It's something of a guess on my side, but I believe the game uses the difference between your and the NPC's Barter skill when determining the prices - an equal Barter level means you buy and sell everything at the same price.

As I recall, in Fallout 1 having Barter above 100% effectively allowed you to exploit the hell out of anyone with goods to trade. Fallout 2 had that intentionally rebalanced IIRC.

I've got about 157% Barter in Fallout 2 (it's most certainly a TAG skill on this character) and find I can get a profit off trade/retrade with most but not all traders. There's a few very cagey bargainers about.
Anything more specific, though? I'm terribly curious.

I don't know the exact calculation, but I'm pretty sure Charisma has more of an effect on bartering than the barter skill itself.

That said, I'm not sure there's been a time when I've ever not had enough cash, and I never put points into barter.

No science here either, but some characters in game state this or that merchant has high prices and I've always taken it in face value, ie. some merchants just keep higher profit margins no matter what.

So I'd assume there's a profit margin first, given by the devs, and only then does the barter (and charisma?) come into play.

Not sure either, if the percentages are set or if there's a roll somewhere (entering the town or something). Might also be, and I'm sure this works this way in some games if not in FO, that certain merchants sell some stuff cheap and some stuff at a higher cost. Like cheap drugs but expensive weapons.

Would be pretty easy to check if you always get the same price differences, like that guy in reno always selling 20% lower than the bartender in klamath. Not going to do that now though.