The Dutch Antilles Guilderalso called Florin is the official currency, but The U.S. Dollar$ is readily accepted. Automatic teller machines are widely available throughout the island, and many machines will dispense Guilders and the U.S. Dollar. Currency can generally be exchanged at local hotels, casinos and places of business. The exchange rate is generally pegged to the USD and stable. It is unlikely for tourists to be taken advantage when changing currency, but it is best to be aware of the current rates prior to arrival.
There are a plethora of random shops and markets around Willemstad offering clothing, souvenirs, crafts, and other goods. These include a commonly-termed "duty free enclave" in the downtown area. Offerings emphasize European goods, to include jewelry, timepieces/watches and linens, plus the usual collection of souvenir shops. Perhaps not noted for great bargains, you may find items at decent prices you'll see nowhere else in the Caribbean.
A water front market lies on the near north side of the main shopping area. It's packed with fresh foods and flowers, best seen or shopped in the mornings.
On Sundays, however most businesses except restaurants in the city are closed.