Seth Godin suggests that big companies make the buying process "screamingly inefficient"- too many layers of approval, endless meetings, and so on. He believes that when you make a vendor an ally you both benefit.
Yet I've read multiple annual reports over the last five years where the purchasing department has been praised for beating up vendors and reducing overall costs. When everything you buy is viewed as a commodity, price is all that matters. But its not. Are you being sent the best quality product? Does it get shipped to you on time? Do you have to pay top price for service as a penalty for demanding a low unit price? Does the added time spent negotiating justify the discount?
It's easy to view negotiations as a zero-sum game, but not if you look past the deal you are negotiating today.