Over the wall, page-240

90% Payment at Port Departure is required such that if the ship sinks, the buyer is responsible and the seller is not left out of pocket. This would be the case under both agreements and spot market sales. General practice.

Once smeltered the $ difference in material composition can be back charged etc. worked out afterwards.

Off the top of my head as an example Iron Ore ships were ~50% payment before docking and 100% before departure. When the GFC hit certain Iron Suppliers relaxed these terms and conditions to get product moving where the buyers could pay in full after shipping was completed.