There are two countries on our tiny island, and - to complicate matters - there are three currencies.

Dutch Sint Maarten officially uses the Netherlands Antillian Guilder, shortened to NAF. This currency of the Dutch islands in the Caribbean is pegged to the US dollar. 1 US dollar is NAF 1.8.

Gas stations show fuel prices in guilders; in supermarkets, guilders and dollars are on the labels. In reality, almost everyone pays in dollars. ATMs offer a choice of currencies. European visitors watch out: The Euro is not accepted everywhere on the Dutch side, and if so, the exchange rates are miserable.

The Euro is the currency on the French side. All prices are shown in Euro, which has a slightly higher value than the US dollar. The dollar is accepted everywhere, many times one-to-one. Therefore, a visitor should avoid paying in Euro, saving up to 10% by offering US currency. The author of this article resides on the French side. Peeking into the cash registers of common (politically incorrect but for clarity needed) Chinese supermarkets - I only see USD currency. 

If you come with Euros to the island and wish to exchange it for US Dollars, the casinos might be the best way to get a good rate. Just walk up to the cashier with the attitude of a big-shot gambler and get rid of your cash Euros.