The most reliable way to prevent Amazon stockouts is to know your lead time and maintain safety stock that covers demand during that entire lead time plus a buffer.
Set reorder alerts in Seller Central at your reorder point — the inventory level at which you must place a new purchase order to avoid a stockout before the next shipment arrives.
Use FBA inventory health reports to identify which SKUs are at risk weekly. Sort by days of supply and prioritize replenishment for items with less than 4 weeks of cover.
If a stockout is imminent and ocean freight cannot arrive in time, consider air freight for an emergency replenishment. The higher freight cost is almost always less than the ranking recovery cost of a full stockout.