If one thing if you are haggling over a used toaster at a yard sale. It's another when you are negotiating a business relationship where the success of both parties is important. A contract with a supplier doesn't do you any good if the terms are so bad it cripples their ability to execute.

That highlights a beef I have with economics. Failure to understand that business relationships are exactly that. You can't model them using the sorts of time invariant non-network models they use.

If you are "negotiating a business relationship" you aren't necessarily haggling on price, but service. This is why I mentioned "the same product"

'The same product' is fleeting and ethereal over the long term.

Yet in the context given, it's timeless and relevant..

Ok, here goes

First, Not everything is a commodity with perfect substitutes, arguably most things aren’t. Substitutability goes beyond price.

Secondly, benefits are not necessarily equal or a linear function of cost.

Third, whether a game is zero, positive, or negative sum requires a look at the costs/benefits of the whole transaction. Saying that a buyer gains $1 more if the price goes up is obvious, it that doesn’t necessarily make it zero sum when you look at the overall transaction of a $1 price raise. .

Zero sum implies that price, costs and benefits are equal. I spend $20 on a product that cost you $20 to make, and I get $20 of benefits out of it.

Whereas I buy something for $20 , it cost you $5 to make, and I got benefits of $100 out of it, that’s positive sum, as both the buyer and seller got positive gain. If you raise the price, the deal isn’t as great, but it’s not zero sum.