Persuasive negotiating lesson

http://www.sfhgroup.com/ca/training/negotiation/
This is a lesson by Allan Stitt of the Stitt Feld Handy Group in how to be a better negotiator and teaches you how to negotiate every day with customers, suppliers, co-workers, business associates and family. You want results in your negotiations but you don't want to fall into the destructive patterns that could damage what could be constructive relationships. You need to make your negotiations effective by figuring out what motivates the other side and knowing when to put an offer on the table. To become a powerful negotiator, you need the skills to handle difficult people and protect yourself from having someone take advantage of you.

How do you get others to "buy-in"? How can you avoid creating long term problems when you negotiate? How can you avoid being taken advantage of in negotiations without creating an impasse?