So I'm GMing Curse of the Crimson Throne and one of the things within there has to do with the turmoil of the city. In Appendix 2 you have states like Anarchy, Martial Law, Plagued, and Unrest.
With each of these states the Marketplace Base Value and Purchase Limit is different.
So during unrest the Base Value is 8,800 gp and the Purchase Limit is 50,000 gp.
So are we saying that during unrest that any magic item under 8800 there is a 75% chance of them finding it and anything over this value is based on the the availability of magic items determined by the community size. Which is a large city, so 4d4 Minor, 3d4 Medium, and 2d4 Major.
So now I roll all these values, determine the item types, and roll for the items.
Now the party has fought some bad guys and taken there items, and sell it.
They then split up the gold and rewards and want to purchase items
Of course everyone wants things like
Ring of Protections
Cloak of Resistance
Belts
Weapons +1, +2, etc
How do you handle it when a player's character has very little in magic items and the items they want are over the Base Value, so it's not a 75% chance and you didn't roll this item.
Do you just give them a different percentage chance of locating it?
Or do you basically say no to every item they want?
It depends on what kind of game you are running. If you want to do things strictly by the book, and use table to determine what is available or not, let the dice decide. If it is unavailable, it is unavailable. They will just have to deal with it like someone would in real life.
If the characters still want the item, have them commission the item and make them wait for it to be made. This is a way to get around the availability issue. Otherwise, let them take crafting feats and make their own items.
In my Kingmaker campaign, one of the players provided me with a backstory that involved him being sent to the Stolen Lands by his church to check it out and report back. He sent word back to them to bring people who are willing to work. He specifically asked for farmers, a smith, and an engineer.
I made the smith a False Priest Sorcerer who is capable of making pretty much anything they can afford. All they have to do is commission it built, wait, and pay.
This is easier than trying to roll up random magic items, or telling them that they can't buy the item they want...
It's a fantasy game. The items are literally crafted by magic. Magic is magical. And the crafting mechanics of this particular fantasy game are so ambiguous as to what you are actually doing, that crafting is like asking the replicator in Star Trek for something...
Player:
"Replicator, I have performed the necessary skill checks, and set aside the necessary funds for resources. I would like a Flying Carpet, please."
Replicator:
"Bleep-Blop-Bloop."
*Flying Carpet fades into existence out of nowhere*
As long as they have the coin and are willing to wait the time, it can probably be bought/crafted... because magic.
I use the ABP from Pathfinder Unchained. It eliminates the need for many of the big 6. You only have to worry about special properties on weapons and armor. This allows more interesting magic items instead of the same boring ring of protection and cloak of resistance. That may solve a lot of your problems.
Now the only thing the characters really need to worry about are build specific items. I found that this tends to reduce the players wanting to sell items. They seem more inclined to keep the od items because their basic needs are already met. Since this option completely removes many of those items there is no reason to sell the oddball items to be able to purchase the staples.
Very carefully.
I've been designing all of my own magic items for a while, now. Even when you're going for that "Bazaar of Wonders" feel, there's just something about players rolling up and knowing exactly what they want and what will be available that takes away from the magical nature of magical items.
I've also been extremely generous with assigning market price value. Paying a premium for one item with multiple abilities, for example, just doesn't matter until you're a high enough level that most of your slots are filled and there's competition for those slots.
Utility is another big concern. Animal Messenger at-will is virtually the same as 1/day; it will only come up in the occasional situation. Whereas at-will Fireball is vastly different from 1/day, and even the latter will generally see use every day.
Then there's the exponential cost increase for larger bonuses. Handing a lvl2 character a +2 weapon will put them way over their WBL, but mechanically, they're only ever so slightly better off than another character with a +1 weapon.
All of this is focused mainly on low-level characters and games; the effects don't matter as much then because there's less resources to go around, so a couple "overpowered" items will make little different. At higher levels, where there are vastly more resources and the total difference really stats to add up, I dial it back.
I don't want to punish characters who want items with cool, unique or unusual abilities because they didn't just stick to what's good, and I want to encourage the sense that magic is strange and mysterious and wondrous.
I use the Automatic Bonus Progression from Unchained so the 'big six' aren't an issue.
Magic items are almost never for sale in any kind of 'shop'. There simply isn't enough demand; most people would take years to scrape up enough money to buy even a basic Potion of Cure Light Wounds, plus it's simply too tempting a target for thieves to have magic items out on display, even in cases.
If you want to buy a magic item, you need to find someone who has one and is actually willing to sell it (unlikely), or hire someone to custom craft it, which will take time. This also gives me some in-world justification for saying someone won't make it ... "Yeah, I want an anarchic unholy human-bane sword." "... no, no way am I making one of those."