The gold from the east needs tempering before it can be sold. The gold from the east is good, it just needs some tempering before it’s entirely presentable. You know, tempering like you’d do in a forge.
The smithy where you’re doing the tempering is pretty fancy, but it’s just a rental (れん). You haven’t sold enough gold to own a smithy as nice as this one yet, so for now, you rent one. It is pretty swanky though, even for a rental.