Earlier quoted context omitted.
If you look at dollar and time amounts, all financial interactions are pretty much zero-sum.
The transaction itself is not zero sum. The existence of the transaction itself is proof that both parties value what they received more than what they gave away (otherwise they would not have transacted). The waste of time is having to haggle to arrive at the price, when the price could have been published. It benefits nobody, because that's the price the transaction would have happened at anyway. But we have to do…
But price discrimination improves cashflow. And these merchants can do the same thing as haggling with less paper waste and on the spot.