At http://www.npr.org/sections/money/2015/06/17/415287577/episode-633-the-birth-and-death-of-the-price-tag, you can hear Planet Money's Episode 633 "The Birth and Death of the Price Tag" from June 17, 2015. It is about how haggling used to be universal, around 1870, we started having fixed prices, but now we are moving back toward more haggling. At 3:30, they mention that in the time of haggling, one group of people did not haggle: Quakers thought it was morally wrong to charge different prices to different people.
I don't recall being taught that haggling was wrong for Quakers. In fact, for me, the epitome of Quakerliness was my great grandfather, and he haggled when he visited the Middle East. I think he saw it as a way of connecting with people, to tell each other the story of what the object being purchased means to you.
But the Quaker principles ingrained in me cause me to favor fixed prices, to feel there is something wrong with haggling, sales, coupons, and gambling. So it was affirming to hear in this stories that I'm not the only person who feels that haggling is unQuakerly.