At your expectation, I have to make an appearance here, and since I'm having more free time in the office this week.
To sum up the quote above, I would say the fair price is the price that clears the market at that point of time. The idea of a fair price is a moot point in my opinion as it is always in a constant state of flux. I need 5 fireshard to craft an item for quest turn-in...so even though the "regular" price of fireshard is 35, I will be willing to pay much more for it at this particular point in time. As for seller, I'm willing to sell this at a higher than normal price because I'm not in a hurry to liquidate that item...the reverse would be true if I want it out of my inventory in a hurry.
I'm going to address the "selling at a loss" point you made. I make something that cost me 100, I sold the finished goods at 50, so I'm making a loss of 50. That defies logical human behaviour...but yet it happens in MMO. Why? Because I get xp for crafting that item. So...do I really make a loss of 50? Or did I just paid 50 for the crafting xp?
When I level my crafter, that's exactly what I did, crafting new recipies and selling them at a loss. I don't think I'm stupid, but I do see it as paying gils to level my craft faster...so it justifies selling the item at a big discount just so that I can liquidate it quick and get part of my money back.
As you've said, and item is worth what somebody is willing to pay for it, and I'm willing to pay for my crafting xp. So even though a business model of selling something below cost does not makes sense (but it does happen occasionally for the reason stated below), it actually makes sense in MMO because of the xp you gain. Even on items that I speculate in the market...there are times where I sell them at a lower price than when I bought them just to get rid of it (failed speculation). Bad traders hold on to their losses...good trader cuts their losses and move on.
Now, on about your comment on Walmart. What people see is that they put some mom and pop shop out of business. What I'm asking here is just to make a fair assessment. What about the cheaper price that benefits the consumers? Especially the lower income group? By saying that selling something cheap/undercutting is bad, you're essentially stating that finding a way to do something more effectively is bad! Heck, steam engine is bad because of all the manual labor that it replaces! Autocad is bad because it reduces the number of drafters a company needs to hire! Accounting software is bad because it reduces the number of job demand for bookkeeper!
What economic studies is the effective distribution of scarce resource, and thus any way to improve that efficiency is good for the economy as a whole. Yes, those who failed to keep up will suffer, just like the mom and pop shops that Walmart puts out of business...but that's just evolution, and evolution is cruel.
The fate of these small shops are a separate issue to be dealt with...a morality issue. I symphatize those that are left out...but they'll have to make a choice there and then....to improve and adapt, or to go extinct. If you are so "anti-walmart" or "anti-big business", then stop buying from them, and get your groceries from a mom and pop shop...no one is stopping you from doing it. If you can't find any, and if you think there's a demand for more expansive items from small time dealers that runs their business less effectively, then open a shop for that. Again, no one is stopping you from doing it.
Society will do what they can to assist these people...but most choose to go all "crybaby" on these structural changes when they fail to adapt, much like what we see in the MMO communities.