Prioritize service coverage (regional delivery windows), infrastructure (dock doors, racking, cross-dock capacity), IT integration (WMS/API connectivity), SLA metrics (order accuracy, OTIF), and scalability (seasonal labor, buffer storage). Also evaluate carrier partners and reverse-logistics capabilities to support returns and omnichannel flows.

Use transit-time heatmaps and carrier route data to compare current versus projected shipments. Assess the 3PL's carrier roster, frequency of departures to your customer zones, and relationships with national and regional carriers. Validate sample lane quotes and run pilot SKUs to measure real-world transit and variability.

Analyze fixed vs variable costs: storage (per-pallet/cubic), receiving and putaway fees, pick-and-pack rates, cartonization and kitting charges, outbound freight accessorials, and technology/integration fees. Include labor escalation, seasonality premiums, and contingency costs for special handling.

Review their labor recruitment and training practices, temporary staffing partnerships, buffer warehousing options, and technology for dynamic slotting and batch processing. Ask for historical peak performance metrics and references showing how they managed spikes without degrading SLAs.