I used to work at a used book store. Since used items are unique, our prices varied greatly.
Customers were always asking us to lower the price, but we had a rule that we couldn't once and item was on the sales floor -- else we'd be haggling all day everyday.
We'd explain this, but people never got it. I wasn't there long before I noticed it was the same few dozen people who haggled.
They never got their discounts, but they never stopped trying.
--The Bagel Of Everything