A recent research summary over on Strategy + Business, which summarized a recent study at UC Berkeley, noted that you can get more by getting mad, as it lets the other party know that the deal could fall through. If the other party wants the deal, this could cause the other party to rethink the terms of the offer and come back with a better deal for you that pays more attention to your demands. However, it can also backfire because if the other party doesn’t want the deal that bad, or if the other party thinks you’re only being angry as a ploy to get a better deal (when you aren’t really angry), it could cause the other party to walk away.
In other words, it’s a tool in your toolkit, but not the centre-point of a strategy that should rely on fact-based total cost negotiations. Who cares if you save an extra 5% on unit price if the logistics costs will cripple you in the end as global freight prices rise again?