Assess WMS and API connectivity, SLA performance (order accuracy, lead time), scalability of storage and labor, security and insurance coverage, and carrier integration. Prioritize vendors that provide transparent KPIs, sample onboarding timelines, and reference clients with similar SKU velocity and order profiles.

Require clear proximity to primary road arteries and freight aggregation points, secure yard capacity for cross-docking, and confirmed partnerships with regional carriers and last-mile networks. Evaluate average pickup windows, consolidation frequency, and the 3PL's ability to offer zoned shipping rate cards.

Build a total landed-cost model including: inbound receiving fees, storage per pallet/day, pick-and-pack fees, outbound carrier accessorials, minimum monthly charges, and seasonal labor surcharges. Stress-test the model with projected peak SKUs and returns to reveal hidden surcharges or volume breaks.

Include measurable SLAs for order accuracy, on-time shipment rate, dock-to-stock time, inventory accuracy, and average pick-and-pack cycle time. Require regular reporting cadence, audit rights, defined chargeback terms for SLA failures, and escalation procedures to protect service continuity.