Most of my "negotiating" has been at garage sales. I almost always ask for a cheaper price. The only time I do not, is when I feel that the person is giving away the item at a "beyond a resonable price," and to ask for more would be greedy. If the person is asking too much, I rarely ask for a discount feeling they are really not interested in "getting rid of" the item. I just walk away. If they are interested in conducting an antique business out of their yard, I am not their target market. (There are some people who choose to sell part of their antique stuff/collections at garage sales, but their prices are almost always more reasonable.)
I have asked for discounts at stores, and most of the time I have asked, I have gotten something off. Unfortunately, it is a rarity.
It goes without saying that politeness works.