From the start, I've been meaning "when sorting things by quali/price" (i.e. clicking on the hyperlink labelled "quality").
And you have been meaning "When you sort by price" (i.e. clicking on the hyperlink labelled "price").
When I click on "price", I do get the NPC listed twice, indeed.
For water, power, and stone, I guess I could click price, since they only come in Q0.
But for any product I want sorted on the marketplace, I usualy want quality along. Out of habbit, it includes my sorting on raw materials. However, for steel, and even more particularly for wood & seeds, it is something I consider a good habbit, as it is common to find Q1 priced cheaper than Q0. You can makes expansions with Q1 mats, but you can't mix Q0 and Q1 of the same material. It has to be all Q0, or all Q1. If you buy some cheap Q1, and it's not enough to make a whole batch / upgrade, you're just stuck with it.
That's why I find the "Quality" link more relevant when shoping for the 3 raw materials above (and why "I'd really love to see the NPC's infinite supplies listed at their proper place when sorting things by quali/price"

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Glad you like the sig =) It's inspired from a funny warning you find here and there on the uncyclopedia, though, each time under a different form, and with variations. For example, the "Charlotte's Web" article mentions:
"Warning: The following text might contain spoilers. This makes the article more aerodynamic, and thus faster. On the other hand, it might not. Just take caution and carry a first-aid kit at all times. 911 is the emeregency telephone number. "
They go as long as:
"Warning: The following text might contain spoilers. This makes the article more aerodynamic, and thus more maneuverable at high speeds. Take caution and carry a first-aid kit at all times if you don't know that Snape kills Dumbledore, Sredni Vashtar kills Conradin's horrible cousin, Maxim kills Rebecca, Santa isn't real, Norman Bates is really the murderer, the prince chooses Cinderella, Riku lives, Maggie shot Mr. Burns, Spike Spiegel dies, Lord Cain's father was doing his sister, Hitler loses the war, Ocelot works for the Patriots, Mister Glass was the mad bomber to begin with, and Soylent Green is PEOPLE!!! "
They also all include a link to the very funny Spoilers article of the uncyclopedia, but honestly, just about all their articles are hilarious =)