When are Unique Items for sale and how do they interact with the rest of the Adventure?

You add 1 Unique Item during a Story Round. If you purchase that item, you will not draw another until the next (different) Story Round in the Adventure.

So, if you return to the same Story Round and you’d already purchased the Unique Item that was for sale, then you will not have a Unique Item available to purchase.

Lastly, if you don’t purchase the Unique Item and you end up drawing a Unique Item during a future Encounter you will not shuffle that Unique Item in as one of the options as it is still for sale back at the store.