I have magic shops, and to those who claim that they are "a silly idea IMO" or "NEVER anywhere to go plunk down cash for items. Bleh." seem to be running campaigns along lines based on their particular mood rather than a rational analysis of in-world considerations. Having no magic shops, to my mind, is DM-metagaming and actually serves to decrease campaign verisimilitude, particularly in a high-magic world.
Even in canon, one can assume that one in four thorps has a wizard, one in two hamlets and three in four villages. One in four hamlets and one in two villages have a wizard of high enough level to generate two additional wizards. Each wizard can scribe scrolls, at a profit of 12.5gp per day, ensuring that if he can get a constant supply of xp (and it's not very hard to obtain that amount of xp i.e. 1 per scroll) he can be assumed to have a good living working just eight days a month. For a practical village wizard, it seems extraordinarily unlikely that he would reject this easy cushy life in place of some austere and non-rational notion that "magic isn't for sale". It is therefore a rational assumption that magical items can be traded for gold.
As for "magic shoppes", I'd argue that the net accumulation of permanent magical items does indeed create a substantial net amount of items. We shall assume a conservative global population of ten million, in an approximately 90% distribution for villages, hamlets and thorps. We will extrapolate that these are distributed in 4

2 ratio, entailing over three thousand villages worldwide, and distributing the rest of the population in a ratio such that four metropolises, ten large cities, twenty five small cities, fifty large towns and one hundred small towns exist worldwide, it can be concluded that on average there are approximately 1200 wizards in the world of 3rd level or higher. We can assume a similar number of sorcerors, twice as many clerics and one-and-a-half times as many druids.
There are thus some 6000 spellcasters in the world capable of crating permanent magical items. Assuming one-in-four have relevant item creation feats, and half are actively adventuring etc., we have 750 "creation-active" casters, and if we are to assume that they craft permanent magical item every six months (very conservative, especially given the nature of the items crafted) we can assume an entry into the market of 1500 permanent magical items per year. Since permanent magical items do not rust or fall apart, we will assume a very low depreciation ratio, and hence assume that half of all magical items *ever* created have been destroyed, and half are languishing in private collections and dungeons. Given a civilisation lifespan of 200 years, there are thus 75,000 permanent magical items in circulation.
I think that that qualifies as a market. I think that there would be magic shops. Sure, they are luxury items, much akin to expensive art galleries today. But to simply flatly say "no magic shops" seems to repudiate basic analysis.