dollar bills vs. dollar coins

Anticipating my Guangzhou metro trip in a couple days (the machines only take 1-kuai coins, not bills), I asked if they had coins at the counter after having dinner.

"冇啊," she said. "有嗰陣時又冇人要。" ("No, and when we do no one wants them.")

I laughed. I guess the preference for light paper bills over annoying, heavy coins is universal (note the reluctance of people in the U.S. to replace the dollar bill with a dollar coin).