Depends on what you are selling and if it is a commodity or unique. A lot will depend on what else is available to them in the marketplace and how you are positioned.
Or, what side of the table you are on... selling or buying.
Also, if you are a salesman and you have to make this sale to get your commission check or you are ever in a position where you can't just walk away. Then you will have a difficult time negotiating. You have the upper hand if you don't 'need' it or have the appearance of not needing it.
If I do negotiate when selling, I always make them give something up. I wouldn't lower the price just because. I made it that price for a reason... the only thing that would possibly change that if I was going to deliver less in features, extend the time line to deliver, or there were some payment terms that were to my advantage eg: Pay 100% today and get a discount.
I'm a big fan of all of jeffery gitomer's books. Here is a post he did about negotiating - but his sales bible, sales answers and a couple others are easy reads and solve all the issues around negotiating so people just want to buy what you have to sell.