I don't know when this started in my game, but didn't notice it until I got to the Boneyard area. When I barter with someone, either a merchant or some random character, I can buy something from them, then turn around and sell it right back for almost 2x what I paid for it. I haven't applied and cheats or trainers, but I'm using the unofficial 1.3.4 patch.
My character's speech is at 50% and barter is 55%. It takes a bit of time to buy and sell back and forth until I have everything. I feel kind of like I'm cheating because a few times I've used this to take every item and all money from a few merchants.

It's normal, they are idiots anyways for living with Regulators and 3 other gangs. And by the way, why do you care? Isn't that GOOD!?

I think the game pits your barter skill against that of the NPC's. I don't think I've ever push the skill above 40% and my characters were still making a small profit from the gun dealers in the boneyards. It was also pretty easy to clean out most the caps in the game just by selling off my loot. This a well known problem with the game's design.
This really isn't that big of an advantage, though. It's not that hard to get everything you need to stroll through the rest of the game.

True. I got insanely rich (21k bottle caps) after wiping out Raider's Camp and selling for items and weaponry. Love my Ripper and .233 pistol. I can afford anything now LOL!!! Tip: If you can't carry all of your items, give them to a party member because oddly they have no weight/ And pick up and leather armor you have. 800 caps per set.