I started to flat-out refuse to offer ANY discount. You should have thought about the price before coming, not try to put a psychological burden on me and force me to discount the product at the last moment.
But yes, in general selling is painful (here in Poland). I find the lack of standardized packaging and shipping prices especially annoying. I could sell lots more if somebody took care of supplying standard boxes with standardized shipping pricing.
People really love when they think they are getting a deal or somehow taking advantage of the seller so it's better to entertain them a little bit if it's going to get the sale.
I always thought that was kind of the standard way of selling things in an informal situation. I just assume everyone's going to haggle or barter so might as well just do it that way. I get the price I wanted, they feel like they got a deal and everyone's happy.
On an aside, my grandma came from travellers. She was probably the best haggler i've seen. She managed to haggle in Sears and places like that successfully. She had this story about being a poor old Scottish pensioner. They also drove across Canada years and years ago with some of her relatives and would set up a fortune telling booth where they stopped. Her sister would case the people waiting asking about their lives, then my grandma would 'tell their fortune'.