Less practicable when the -- ehem -- Good Folk are dealing with each other.
True, the leprechaun did have its gold. And with all the glamor in their magic, real things might really have value for them. It's not difficult to exclude alchemy from the things they can do when it's never been in the folklore.
That would leave me only the issue of how a young selkie can acquire enough to become a suitable suitor for a young woman of noble fae blood. One in the navy. Where they have started to build their ships of oak, when eggshells and acorn caps were once good enough for anyone. . . .
Having him claim his share of the prize money is one possibility. Having them hunt down sea dragons and divvy up the hoards is another.