Ah yes, concerning that: hagglers. Especially the arrogant ones who know you're not in charge of the prices and demand to see the chef so they can make some kind of a deal for a discount. Please die. Or move to a country where it's part of the local culture.
Can't help but sharing this with you though: a friend of mine also works in retail and she also has to deal with hagglers, and a lot of them use the "I saw it at a lower price in another store" argument to get something for cheap. Everytime she hears that, she just flatly tells the customer they should go to that store and buy it there, and her boss simply approves of it. She even went as far as telling a customer to fly to India because the item in question is cheaper there.