Customs and VAT Procedures for Consignment Import (Non-payment), Resale, and Export

I am planning to conduct business using a consignment import method, but since it is my first time, I am curious about the detailed procedures. The business structure is as follows: We bring in goods from an overseas seller in the form of consignment import (non-payment/no charge) and store them in a domestic warehouse (not a bonded warehouse). Once domestic or international buyers appear, they pay us for the goods, and we then use that payment to pay the overseas seller for the items. 1. Do customs duties and VAT occur when declaring consignment import? 2. When the actual payment is made later, do we need to proceed with a formal import declaration again, and will new customs duties and VAT be incurred at that time? 3. After the consignment import declaration, if we eventually export the goods to an overseas buyer (export declaration), what procedures should we follow? 4. I understand that the customs duties paid in this case are calculated differently than based on the invoice amount; is it possible to receive a refund when we export the goods later?