If all the Lauan Shield's are bought out one day, they may not be in stock the next day. I noticed this after I went to buy a few to make into Leather Shields and saw they were all purchesed. I went back the next day and they didn't appear on the list at all.
maybe it can . . . cuz i know according to yor fame or levels or something, difference things are offered to you as you gain them. imnot sure if its a level thing or a fame thing.
*personal experience* in san d, i was told raimbroy sold dried marjoram and some other stuff but when i looked he just a couple things so i went all the way to windy. when i checked out the grocery store again at a later time, more fame and higher level, he had a buncha new stuff available. same with the bait shop lady.
main factor so far as I know is what areas the nation has under control, as was just said.
One week I went to the music shop in Bastok Markets and they had like 4 things for sale.. I go back after the conquest update (having done no extra quests or missions) and they have about 12-14 things for sale.
It's just like how there are merchants that sell items from specific parts of the world but cannot sell if your nation doesn't have control.
But in this case, it has nothing to do with any of that. Cauzeriste is a guild shop NPC, and if no one is selling Lauan Shields to the guild or someone bought all of them from the guild, then there won't be anymore for him to sell. Guild shops have limited supplies, unlike normal NPCs.