Sammael said:
From 5th to about 9th level, characters have enough wealth that they should be able to purchase, commision, or upgrade their magic items. However, any one of those methods can be an adventure unto itself - looking for a powerful spellcaster, traveling to a major city, doing favors to people, etc.
I often begin campaigns at about 5th level.
From level 10 onward, characters have enough power, influence, and wealth that not letting them just buy magic items completely suspends realism. The party has access to legend lore, teleport, locate person, whatever... clerics are now bishops and can damn well order accolytes to make them magic items; rogues practically run thieves' guilds; bards probably entertain kings and archdukes; wizards are guildmasters and sages; and fighters have probably saved their comrades' buts many, many times, and can expect to rely on their connections.
This is the point at which I begin letting them "quest" for magic items as they begin to know the legends of powerful artifacts and the histories and clues that might lead them to the items.
Clerics in my campaigns don't advance because they are higher in level. I don't feel that makes much sense, as they are always away. I see them more as chaplain crusaders, favored by their chosen deity to perform miracles. In a sense, they are beyond and above the mortal hierarchy of the church, yet still controlled by it to a certain extent. This can vary by church, but this is the most common way I do things. In my Kingdoms of Kalamar campaign that just ended, there are actually a nice set of rules to control advancement through the church seperately from that as a cleric. You can choose to expend XP to gain influence and control in the church, or you can go independent. I had one player who rose moderately within his church and attained several acolytes and an administrator to help him with his duties. I digress, but basically just because a character is high level does not mean he has influence over others. Conversely, a wielder of influence might be a charasmatic Commoner 1 who was in the right place at the right time.
If you allow Clerics to order acolytes to make magic items, then do you ever have the church order the PC to make magic items and give them up? It's the only fair way of going about it.
As for wizards, they tend to create strongholds, but as they are never home, they hold little influence over any single individual. Bards tend to be traveling minstrels, renowned through many regions and invited by kings to perform, but neither is obligated to the other, as the PCs are usually outlaws (in the literal sense). Fighters would only hold influence if they controlled armies, and few of my players have ever been interested in becoming that indirect in playing the campaign (I've had a few players who are interested in that sort of thing, but they do not play fighters, so they use their funds to purchase land and influence to gain title, power, wealth, and armies - nevertheless, their holdings are dwarfed by any real kingdoms).
Basically, in my campaigns, personal power does not equate to political influence except in the most militaristic or violent cultures. To me, it's like saying the United States Army Special Forces or Navy SEALs should have political influence over the President. It doesn't make any kind of sense.
To cover one obvious retort, if the kings and nobles are afraid of what the PCs have the ability to do, then I liken that to a country capitulating to terrorists. Again, this is not something that makes any real sense.
In other words, my campaigns are such that by the time the PCs have enough money, they can pretty much expect to be able to obtain nearly any item they can afford, and I don't waste their time by requiring them to roleplay shopping trips.
I make sure the attainment of a magical item is never so trivial as to be referred to as a shopping trip in the first place.