I'm still pretty new to the game, but I have gotten to the point where I am shopping around for new items / stuff for crafting.
The vendors in Haven for example, their inventory changes correct? How often does this happen? Is it day to day or something?
I believe it is once every 24 hours server time.
If you have multiple characters, I think they also get different shop inventories.
Not too sure about that.
But it used to be that every player saw a different shop inventory.
Kozma I believe is the only vendor in the Haven Bazaar who's inventory does not rotate.