Find GT Qlvl:
http://classic.battle.net/diablo2exp/items/exceptional/katars.shtmlfind the highest affix you need to spawn:
http://diablo.gamepedia.com/Affixes_(Diablo_II)cross reference them to find the ilvl required for it to be able to spawn:
http://wiki.theamazonbasin.com/index.php/Affix_level_chart#TableKeep in mind...
ilvl = character level + 5 when shopping, capped at 99. In Normal difficulty, there is a further cap, depending on which Act the vendor is in:
Act 1 : 12
Act 2 : 20
Act 3 : 28
Act 4 : 36
Act 5 : 45
The ilvl of shopped items must be 25+ for an upgrade to occur. The chances of an upgrade are as follows:
Exceptional upgrade in Nightmare: ((ilvl * 64) + 4000) / 100,000
Exceptional upgrade in Hell: ((ilvl * 128) + 5000) / 100,000
Elite upgrade in Hell: ((ilvl * 16) + 1000) / 100,000
This is all the info you ever need to shop anything.
Clear eyes, full hearts, can't lose