Companies must make an inward declaration for all goods imported into Singapore.  All imports require an import permit although this is largely a statistical requirement for most goods.  Details can be found via Singapore Customs.

Bona Fide Trade Samples

The import of trade samples that is below US$300 is not subject to payment of duty and/or GST.  In addition, no permit is required for their import.  Bona fide trade samples (excluding liquors and tobacco) may be imported for the following purposes: solely for soliciting orders for goods to be supplied from abroad; for demonstration in Singapore to enable manufacturers in Singapore to produce such articles to fulfill orders from abroad or by a manufacturer for copying; and for testing or experimenting before producing such articles in Singapore.  More information can be found via Singapore Customs.