the general rule is the bigger the item or the smaller the store, the easier to bargain. You can always get deals if there is a salesman working at the store because most of them are on commission, some of them don't even have base salary. The salespeople would usually get commissions from both the store(for selling any item) and the manufacturer(for selling a particular item) It is best if you know the market value of the things that you are interested so nobody can rip you off. If you don't,
ask nicely, "can you give me a good deal?" if it is big item such as furniture(Brick, BadBoy), laptop(Future Shop, Best Buy). if it is a small item such as shoes, or even small things in the dollar store, ask them "can you give me a cheaper price?" or "can you give me these for $__?"
If they say no, say thanks. take it as it is or leave it. If somebody laughs at you, screw them, they are stupid. He who never negotiates is always the nice guy who gets screwed over.
You will be surprised at how much you can negotiate and save! It feels good! Also, the garage sale is the best place to practice your negotiation skills! Let the fun begin!