Take someone there who can hide between purchases, he'll rarely log out on you and doesn't let anyone know someone is buying from the alchemist. Some restock times vary, as quickly has half an hour to two hours, typically one hour. I do the buy session a couple times a year. I've had someone start buying the vendor out on me as well. Had to wonder if my crafter Landreu being busy at the house for hours on end made someone curious what Tanivar might be up to.
Got a rune to a ship at the Sea Market on my mailbox. The house with a lighthouse on the west coast of Zento.