Mo NPC

I think it's because they can't put activation parameters on a regular store. This goes for Jane too, you have to finish her quests and buy things one by one. Although, I don't see why they can't put a value box in there after selecting your item =/

I could always buy sets of pots from Jane...and yeah, as Cyanne said, Alacaster sells sets too. Think of the inflation if you could only buy 1 rock at a time and people are lazy and just go fm to buy rocks for 10k each or something xD