When I was shopping in Hell games, regardless of the act I was in, all that seemed to spawn was light gauntlets and gauntlets (and their exceptional/elite version).

So I decide to try a Nightmare game: in act 5 and 4, the majority was still light gauntlet and gauntlet. But when I move to act 2, chain gloves started to appear.

Now my question: what determine the basic item type that a vendor have? Is it hardcoded into game what item appear in which act? Or is it determined by the clvl of the character that refresh the vendor stock? The second option seems unlikely since I was shopping with the same character in both game.

Maybe some technical expert can help here?

the ilvl available is clvl + 5
in normal, the ilvl is capped. iirc it's 12,20,28,36,45 for acts 1-5 respectively.

i think the ilvl is capped so you can't buy elites in NM, but i don't know what it is off the top of my head.

heavy braces are ilvl 43. so make sure you're lvl 38 or higher. they should be sellable in act 5 normal and on.

i hope this helps.

You can only buy such Elite items from NPC:
(Maybe There are some flaws,cuz I made it myself:).If anyone finds
something wrong,plz point it out,thx).
¡ñAct I:No elite item can be spawned.
¡ñOther Acts
Weapons
============================================
War Spike ---Fara---Hralti---Halbu--Larzuk
Berserker Axe ---Hralti ---Halbu --- Larzuk
Decapitator ---Fara --- Hralti
Champion Axe --- Hralti
Glorious Axe --- Hralti,Ormus ---Halbu --- Larzuk

Lich Wand --- Drognan--- Ormus --- Jamella --- Malah
Unearthed Wand --- Ormus --- Jamella --- Malah
Caduceus --- Ormus --- Jamella --- Malah

Thunder Maul ---Halbu --- Larzuk

Phase Blade ---Drognan --- Ormus --- Jamella --- Larzuk
Mythical Sword --- Hralti --- Halbu --- Larzuk---Malah
Champion Sword --- Hralti --- Halbu --- Larzuk
Colossal Sword --- Hralti --- Halbu --- Larzuk
Colossal Blade --- Halbu --- Larzuk

Fanged Knife --- Fara --- Hralti--- Halbu ---Jamella--- Malah
Legend Spike --- Hralti ---Halbu---Jamella--- Malah

Ghost Spear --- Fara--- Asheara --- Halbu
War Pike --- Fara ---Asheara --- Halbu --- Larzuk

Cryptic Axe --- Hralti --- Halbu
Great Poleaxe --- Hralti --- Halbu --- Larzuk
Giant Thresher --- Halbu--- Larzuk

Shillelah --- Drognan --- Ormus --- Jamella --- Malah
Archon Staff --- Ormus --- Jamella --- Malah

Ward Bow --- Asheara --- Jamella --- Larzuk
Hydra Bow --- Jamella --- Larzuk
Colossus Crossbow ---Asheara --- Jamella --- Larzuk
Demon Crossbow ---Jamella --- Larzuk

Feral Claws --- Hralti---Asheara
Runic Talons --- Hralti --- Anya---Asheara
Scissors Suwayyah ---Halbu---Jamella --- Larzuk---Anya

Winged Knife --- Fara --- Asheara --- Halbu--- Malah
Winged Axe --- Fara --- Asheara --- Halbu --- Malah
Ghost Glaive --- Fara --- Asheara --- Jamella ---Anya---Malah
Winged Harpoon ---Halbu---Jamella --- Anya---Malah

================================================

Armors:
================================================
Giant Conch ---F--- As
Spired Helm --- Har---As--- Hal--- L
Corona --- Har --- Hal---J --- L
Demonhead --- O --- J

Hellforged Plate ---Har--- Hal---J--- L
Lacquered Plate -- O --- Hal--- L
Shadow Plate ---Hal--- L
Sacred Armor ---Hal--- L---An
Archon Plate ---Hal ---L---An

Aegis --- F --- Har--- Hal---J--- L
Ward ---Har--- Hal--- L---An

Crusader Gauntlets---F --- As--- Hal--- L---An
Ogre Gauntlets ---As--- Hal--- L---An
Mirrored Boots --- F --- As--- Hal--- L---An
Myrmidon Greaves--- As--- Hal--- L---An

Bone Visage ---Dro--- O --- An
Troll Nest ---Dro--- O --- An
Blade Barrier ---Dro --- An

Notes:
F=Fara
O=Ormus
Dro=Drognan
As=Asheara
Har=Harlti
Hal=Halbu
J=Jamella
L=Larzuk
An=Anya
================================================

As ScoliosisMan said, ilvl = clvl + 5, with caps in normal (see his post). The game will build a list of items wich have at least 1 in the <npc>Max column in weapons/armor.txt file. Items that have qlvl higher than ilvl, will not spawn

If ilvl is less than 25, there's a 1 / (MagicMax + 1) chance that the item will skip the "less-than-magic" quality selection, where the chance to be upgraded from normal to superior is: if ilvl >= 10, 25%, else 15% (also, if the ilvl is less than 5, there's a 10% chance that it'll be low quality). The game will select the quality for a number of MagMax items this way. After that, the game continues to where it would have been if it had skipped this section.

Now the game will attempt to create the item with magic quality. There are two restrictions to this: 1) bitfield1 must be an odd number, 2) <npc>MagicLvl must be lower than ilvl. Number of magic items to create is rnd<(<npc>Max + adder)> + <npc>Min. Adder is 1 if ilvl is less than 25, else rnd<3> + 1.

After the quality has been chosen, it'll do the difficulty and excep/elite upgrading. The game will skip all upgrading if clvl is 25 or lower (iirc, in the beta this check wasn't done, and you could buy normal/socketed elite items with low level characters in Hell). If in nm, the chance for upgrade to exceptional is:

chance for excep = (ilvl * 64 + 4000) / 100,000

If it fails to upgrade to exceptional, it will use the item in NightmareUpgrade column.

In hell:

chance for elite = (ilvl * 16 + 1000) / 100,000
chance for excep = (ilvl * 128 + 5000) / 100,000

It will only upgrade to excep/elite item if HellUpgrade column is blank (or "xxx"), else use that item.

There's a separate code for misc items, wich I haven't look at yet. Maybe someone else knows the details of how they are spawned. I also haven't looked at how it determines if the item should be socketed.

Please let me know if there's anything missing or incorrect in the text above. As I said, I haven't looked at the code in much detail so I might have missed something.

Edit: Minor correction about NightmareUpgrade