Image by Dean Lewis from Pixabay
Magic items are a core part of any fantasy RPG. For many players, gaining powerful magic items is far more important to them than finding cash treasure. The neccessity for magic items and their availablility varies significantly across various rule systems, and in different editions of each set of rules. But there seem to be two key approaches;
Magic Items As Rare Heirlooms
The first approach is that magic items are rare and unusual. They are family heirlooms, or found in the deepest dungeons after numerous perils have been overcome. You can't just pop down to the market in any town or village and pay cash for a magical sword.
Something I really like about this approach is that magic items are exotic things that keep their mystery. Swords and shields may have names and be unique rather than being mass-produced by any character with the right skills and a bit of time on their hands.
The downside to this view of magic items is that it works best in a setting where the vast majority of opponents can be taken down with skill, cunning, and a bit of luck. If there are enemies who can only be defeated by magic, the DM needs to ensure that the players have access to that magic in a consumable form - spells, scrolls, potions etc, to avoid creating situations where they have no way to win.
Magic Items As Commodities
The other main approach works for more "videogame" rule systems (D&D 3.5 is a prime example) where magic items are expected to be plentiful and by mid levels players expect to have every available slot filled with a magic item of some kind.
In this kind of setting, there are many monsters that can only be hurt by magical weapons, and many challenges which need magic items to overcome them. But the items are plentiful. Many monsters will drop them after even a medium challenge combat. There will be magic shops in any large city which will sell you what you want if you have enough cash, and are happy to buy or exchange surplus items (either picked up on adventures or because the players have upgraded them). Many players will also have feats or skills which enable them to make magical items.
This view of magic items effectively treats them as just another form of equipment; the magic item shop is just another kind of hardware store or gun shop. It can lead to exciting campaigns where players get to tackle extremely capable opponents with a good change of winning.
But the downside is that magic items lose their mystery, and it can lead to the kind of power creep where medium to high level players have to be booted off to adventure on other planes to avoid too much damage to the "home" world.
An Attempt To Control Magic Item Proliferation
In my own homebrew world, I have attempted to find a happy medium between these two approaches. It's mainly played in D&D 3.5 and 5th Edition. 3.5 tends to be a magic-item heavy system, while 5th Edition has dialled that back a bit.
The logic I have used is that because it's a very "political" world, with a lot of the action driven by inter-state rivalries, governments try to acquire all the magic they can to equip their armies. Item creation is heavily licensed; most governments expect all items created to be handed over to be used for the good of the state.
This means that adventurers are left with the dregs plus what they can find on their travels. While there are no magic shops, there are plenty of NPC sponsors and quest-givers who will lend (but rarely give) items of use in a specific quest. They will also arrange trades of items a party finds but can't use for items they can.
These measures keep the level of magic power under the DM's control. Players can't just browse through the most obscure rulebooks and say "yeah, I pick up XXXX item in the shop". It is especially helpful in keeping items with higher plusses out of characters' hands until they get to a decent level. Magic is no longer a function of how much gold the players can loot.
However, it has led to a few situations where players (especially those who are used to just shopping for all they can afford) get really pushy and demanding, throwing toys out of the pram unless they can have a specific item.
Overall, I am not sure this solution has worked very well, I'd love to hear better ways to help magic items keep their mystery !