The Collectors

Nella's merchant guilds cover most of the goods anyone might need during their lives. From livestock, medicine and food, to weaponry and even airships. If a person wants to obtain any given object, or person in some regions, one of the merchants will be able to offer what they seek.
This however comes with one problem, what if someone is unable to pay the price that was agreed upon. In this case, the collectors are summoned. These are special branch of law enforcement that specialize on the collection of debt. These officers have a variety of equipment at their disposal to ensure that the merchant that is owed, will recieve the money, one way or another. The collectors will first try and find the criminal on the island the crime has been committed. Should that result in them capturing the person in question, they would be held in prison, while the unit would venture to the residence of the indebted, investigating every single bit of their belongings before selling it in an effort to accumulate the money needed.
Should that not be enough, the criminal will be forced to work to pay the money back. Either in the service of the merchant they are in debt to, or in a government owned labour camp that would pay the prisoners salary to the merchant instead, until the debt is paid off in full, including interest of course. Should the debt not be repaid in full, either because the criminal managed to escape, or died in the labour camp before they could accumulate enough money, the government will give the merchant half of the remaining debt. This security led many accomplished traders and craftsman to move their shops to one of Nella's islands. This slowly pulls away all trader from the other nations, causing the trade nation to already have a monopoly on some rare items and products.