Garage Sales - Haggling Anyone?

I had a lady whose culture is known for haggling over a price come with me to go garage sale hunting. She advised to see if you can get the item for 50% off, then see what price the vendor gives you for a counter offer. He might come all the way down or might come down a long way off the asking price. He might be someone who has a bunch of goods, but all of them are way overpriced.