I've meditated on this a little more and I think part of what's going on is a perverse selection process in who you're likely to be negotiating with. Since most Americans seem to feel a bit icky about haggling and negotiating, they're going to avoid careers doing it.

Negotiation heavy jobs are then going to draw from whoever doesn't feel whatever weird shame the rest of us do. Well, it's no surprise then that our negotiations are often us vs some sociopath trying to scam us.

If bargaining/haggling/negotiating were more of a normal part of our culture, then more honest people would be involved in negotiations and they wouldn't seem so scammy.