In a recent article from Computer Weekly it discussed the recent trend of clients demanding large discounts from providers, sometimes up to 24%. This is counter productive as large discounts will only harm the relationship in the long term. Negotiating a ‘win, win’ scenario means that everyone is happy in a relationship. If your vendor is actually loosing money throughout the lifespan of the agreement they will attempt to re-coup losses. This may mean a reduction of quality in the form of staffing levels or technology improvements. No company acts as a charity for another. Thinking you have screwed the vendor in the negotiation only means you loose in the long term.
Much of this is stated in the article. You can read the full article here