The pirate ship boutique is the place where, for security reasons, the pirates sell their wares from aboard their ship. Doing so provides privacy for illegal transactions, and it is the easiest way for the pirates to stay mobile, avoiding arrest. Full of rare, exotic items from around the world that the pirates obtained through "high risk trading", otherwise called stealing, the pirate ship boutique is a must for a treasure hunter.
During waterbending training in the waterfall lagoon, Aang accidentally washed all of the team's supplies down the river, forcing them to go into a nearby town to purchase new ones. While they were looking for supplies in the seedy merchants pier, they were approached by Pirate Barker Oh who persuaded them to peruse the boutique. Aang, Katara, and Sokka entered the ship and browsed through the collection of curios. It was here that Katara discovered the pirates were in possession of a waterbending scroll. She wanted to buy the scroll, but their funds were insufficient, so she ended up stealing it in her desperate need to learn waterbending.