In La batalla por el dominio del Caribe y el Golfo de Mexico (series in 3 volumes), by Jose Luciano Franco, Curacao is mentioned as an important entrepot by the early 19th century. Not 100% sure if this also applies to the early 18th.

Basically, the Dutch would bring goods to Curacao and ships from other nations would make purchases there and then under their own flags ship the goods to their destinations.

For example, say a Dutch trader brings in a bunch of fine Dutch cloths from Europe. They would bring it to Curacao and wait for French, Spanish, or English merchants to come in, buy up goods, and then ship out. The French ship would take the goods to French ports, as it was authorized to do. But they'd either lie about the origin of their goods, falsify the bill of lading, bribe customs officials, etc.

Another common strategy by the early 19th century was to claim some kind of distress requiring coming into port as a matter of life or death. For example, water shortage, emergency ship repairs, lack of food, etc. Once in port, they could then sell off goods in order to defray the 'costs' that they had incurred in order to fix whatever 'emergency' they had used in order to receive authorization to enter in the first place.

They'd then sell more than they needed, whether by light or by offloading goods in the middle of the night, then ship out again.

Colonial officials should have pieced this together, so I really doubt they were in the dark about all these 'emergencies' foreign ships kept having. Some may have been bribed, other may have seen it as a necessary evil to keep locals happy.

Finally, you could also just offload on some abandoned coast or on land that was the property of the person to whom you were selling directly.