"So, a lot of people really hate what they call 'price-gouging', when there's a shortage of something and the price of it shoots up. And of course it mostly looks, to a typical consumer, like it's just a seller taking advantage; the buyer imagines that they 'already had' the right to buy something at the price it was yesterday, and not having it any more feels like a loss. They did have that right - yesterday. Once it's scarce the price changes. But let's suppose something goes wrong with the Sphinx River - suppose it flows backwards for a day or something in some kind of magical disaster, and it's all salt close to the coast till the situation's resolved. Because and only because you can then charge more for water, some clerics will trek downriver - well, in this situation I suppose it's upriver - even if it's dangerous to get on a boat, even if they were busy, even if they were retired, because they want the money. So then Sothis has more clerics who can make water than it had yesterday, precisely when it needs them. The river returns to normal, they all go home, no one's died of thirst and everyone is paid for their trip and their orisons.
"And suppose your guild sets a minimum price - so much for a yard of plaid, say. And then you get a great deal on dye. You take it, obviously, you'll save money that way and have a little extra, but the customers never see a speck of it. You can't outcompete your guildmate, and you can't say 'today we have a special on anything in blue'. And meanwhile, people buy less fabric, because it's expensive. Could you be selling twice as much at three quarters the price if you hired more people, making more money and giving everyone more clothes? You'll never find out! There could be someone with their nose pressed up against your shop window thinking 'if only some of it was a little cheaper I could justify one square of it for a scarf' and their favorite color could be blue and you'll never know!"