Demurrage prevention can be tied to payment milestones, but each milestone must be tied to objective materials. The contract should list the required declaration-elements sheet, duty and tax calculation, release conditions, agent confirmation email, and reviewers; release the related payment only after the materials pass review. Splitting payment into installments without evidentiary conditions still will not prevent gaps in declaration, valuation, or inspection information from being discovered only after arrival. Follow customs decisions made by licensed local agents and customs authorities.
For an adjacent issue, see What pre-shipment checks are useful for cars that will operate in desert and high-heat conditions?.