Inquiry regarding the meaning of "import for sale purposes" when importing sample PCB boards

I am currently in a situation where I have commissioned a Chinese company to manufacture test samples of PCB boards prior to product development. While researching related information, I found that even if the goods are valued under USD 150, if they are subject to exclusion from manifest clearance and are being imported "for sale purposes," a formal import declaration must be filed and taxes must be paid. I am curious about the specific meaning of the expression "imported for sale purposes." Does this refer to cases where the imported goods are intended to be used as components of a finished product for sale, or does it refer to cases where the imported goods themselves are sold as-is?