Finder's Keep sells rare items, mostly species-exclusive items such as Hydro Jaws. Other uncommon items are occasionally put on the shelves, but not often.
Finder's Keep was first introduced when Lake passed by. The owner, who had then been unnamed, offered him a Hydro Jaw. Lake would have been willing to buy, if he'd had any money.
Later, the store was robbed by the Booster Trio. Jazz woke the owner up and directed him toward the thieves, which he promptly chased and retrieved his goods from. Upon returning, he discovered that Jazz had watched over the store for him, so as to avoid further theft. This prompted Relic - as he had been named then - to hire her as his assistant.