The 3.0 DMG (not the 3.5 revision, though, for some reason!) suggests to reduce the frequency of magic items, and that there are no shops where to buy them.
Where is this in the 3.0 DMG?
EDIT: Found it, pg 164. It doesn't exactly suggest this. It is under the section for creating "diverging worlds" such as stone age or rennaissance and also has suggestions for running both a lower
or higher magic world:
"Another way to create a divergent game is to change the amount of
magic available.
Low Magic: In a low-magic game, spellcasters and magic trea-
sure are about twice as rare as normal. Magic items aren't for sale
because they're too rare to ever think of parting with for mere gold.
The occasional trade of an item or its sale for gold is possible, of
course, but it is a rarity in the economic structure.
Common people almost never see magic. Some might not even
believe in it. A spell or a magic-using creature completely bedevils
the common folk and terrifies them. All magic-using creatures,
including characters, may be thought of as "demons." They might
be persecuted. Witch trials and the like could be a common fate for
wizards and sorcerers. Clerics and other divine spellcasters are
probably safer than arcane spellcasters, but they might not be,
depending on the culture.
High Magic: Spellcasters and magic treasures are twice as com-
mon as presented in these rules, if not more so. Most characters
have a level or two of wizard or sorcerer. Even a shopkeeper might
be at least a 1st-level spellcaster. Magic items are bought and sold in
clearly marked shops like any other commodity. Spells are used to
light homes, keep people warm, and communicate. The function
they serve is as commonplace as modern-day technology is in the
real world.
This sort of campaign can be directed one of two ways. The first
is to take the world of the utterly fantastic route, where magic is
sophisticated and common, and to create a world unlike anything
anyone but you has ever imagined. The second is to take the comi-
cal route, where magic simply becomes technology—little imps in
boxes perform calculations like computers, and people have magi-
cal transmission television sets. The second route can be fun, but
the sort of light-hearted parody it leads to is probably not a good
basis for a long-term campaign."
Perhaps this was removed from 3.5 DMG because, as much as some of us hate to admit it, doubling magic items or halving them with no other considerations recommended will result in some pretty screwed up encounters. Either your party is bulldozing every single encounter with no fear or the opposite is happening to them. This would be true in just about any edition of the game. It just isn't a good recommendation as written.
The defualt assumption the 3.0 DMG gives is this though, which is the same as the 3.5 DMG:
"Unless you are going to run a divergent game (see Differing
Magic, page 164), magic is prevalent enough in the world that it
will always be taken into account by smart individuals. A merchant
wouldn't be flabbergasted by the idea that someone might try to
steal from her while invisible. A swindler would be aware that
someone might be able to detect his thoughts or his lies.
Magic shouldn't be something that common people are unaware
of. Spellcasters may be fairly rare in the big picture, but they're
common enough that people know that when Uncle Rufus falls off
the back of the wagon, they could take him to the temple to have
the priests heal the wound (although the average peasant probably
couldn't afford the price). Only the most isolated farmer might not
see magic or the results of magic regularly."