The Sigil said:
Working up a treatment of "the Economy of Magic Items" but let's take a real quick look at a couple of things here. Posting from work, without the DMG, so had to rely on Jamis Buck's generators - took the MAXIMUM found in each with 10 runs and rounded up... if you're easily bored, skip to the last 5 paragraphs.
--The Sigil
to quote the DMG page 137...
"To determine the amount of ready cash in a community, or the total value of any given item of equipment for sale at any give time, multiply half the gp limit by 1/10 of the community's population. For example, suppose a band of adventureres brings a bagful of loot (100 gems, each worth 50gp) into a hamlet of 90 people. 1/2 the hamlet's gp limit times 1/10 of its population equals 450. (100/2=50, 90/10=9, 50x9=450)"
Small town, pop 1000..... 800/2=400, 1000/10=100, 400x100=40,000gp. you can sell most of your stuff in a small town, as long as you dont mind copper, and dont keep coming back. I'd rule the pricyest single sale a player could make would be about 1/10 of this to a single buyer... so around 4000gp. my ruling, of course is mine....
Large town, pop 3000.... 3000/2=1500, 3000/10=300 1500x300= 450,000gp, so even with my 1/10 idea, 45,000gp is almost any item.
So for a Large city, pop of 15,000..... 40000/2=20000, 15000/10=1500, 20000x1500=30,000,000
You could sell anything in a large city.
joe b.
ps. Agback, considering the disparity between the purchasing power and the production ability of magic.. magic would sell like hot-cakes in a 8,000 or so greater population. No need to worry about that ring sitting on the shelf...

and given my experiece in third world countries, the idea that somthing may sit on a shelf for five or so years is not unusual.... (even food items

there really is a different mentality about business outside of the "developed" countries