It depends on the circumstances of the case. Generally speaking, in the case of insolvency, you should immediately register the debt against the buyer with his liquidator/administrator/trustee, as applicable.
In the case of a protracted default, you should send a strongly worded letter to the buyer demanding for immediate payment. You may also arrange, through your bank, to have the bills protested against the buyer if you considered that this action is effective. If no amicable settlement can be reached, you need to take loss minimisation actions including but not limited to the appointment of debt collectors and/or the institution of legal proceedings against the buyer.
In the case of repudiation, you should first arrange proper storage of and insurance for the goods involved. Then you should send a written demand to the buyer to take delivery of and pay for the goods within a certain time limit. If such action fails, you should look for alternative buyer(s) for reselling the goods in order to minimise losses if, in your commercial judgement, this is the best course of action and hold the original buyer responsible for any losses incurred. You should obtain HKECIC’s prior approval before resale/disposal of the goods.