Granted, "Tips for Getting the Best Deal from Vendors," published by ComputerWorld in PowerPoint format is a bit overproduced. (Couldn't these have been a nice little article, with each tip as a bullet point? Actually, it is, but somehow you're supposed to use the PowerPoint to integrate your own points and present to some presumably executive-level gathering.) That said, you'll find some jewels from master negotiation trainers, such as this one from Roger Dawson, author of Secrets of Power Negotiation:
Never offer to split the difference
Instead, try to get the other side to offer to split the difference. “How far apart on this are we? We’re not that far apart. There must be some middle ground on which we can both agree.” When they offer to split the difference, you can reluctantly agree to their proposal, which serves their perception that they won.
Danger point: If you offer to split the difference, they could get you to split the difference again.
Solution: Get the other side to offer to split the difference. You may be able to get them to split the difference again. Even if you don’t, you still make them feel that they won.
The slideshow is part of a larger presentation on the topic of managing vendors. You'll find the table of contents here. (My preference: That they'd make this available as a downloadable PDF, so I don't have to go tooling down a bunch of separate and tiny paths.)