Start the transition planning 60 days before your target go-live date. Use this time to select the 3PL, sign contracts, provide prep specifications, and plan inventory transfer logistics.
Do not attempt to transfer all inventory at once. Start with one product line or channel — test the 3PL's receiving accuracy, prep quality, and outbound timing on a small batch before committing full inventory.
Maintain self-fulfillment capability during the transition period as a backup. If the 3PL has a receiving delay or quality issue in the first month, having backup fulfillment capacity prevents a complete service failure.
After the transition, compare 3PL performance metrics to your self-fulfillment baseline: error rate, dispatch time, prep accuracy. A 3PL that performs worse than your self-fulfillment operation is not the right partner.