Negotiation

In our sales meetings we have been working on negotiation skills. I often hear and see Account Managers shifting the power in the meeting away from them by being overly apologetic, getting too excited, talking past the close, easily giving concessions, formally addressing the client out of respect without receiving the same back, etc.  If any one knows of an article outlining the mistakes sales people make that give up their power in the negotiation, or do's and don'ts for maintaining equality in the meeting, I would love to see whatever you can direct me to.  I feel like I have been looking all day with no success :(