Prioritize measurable KPIs and infrastructure: SLA-backed order accuracy, dock-to-stock times, inventory visibility (real-time WMS), cross-dock capability, and labor productivity. Also evaluate carrier integrations, peak-season scalability, and whether the 3PL supports kitting, returns processing, and omnichannel order routing to reduce cost-to-serve.

Location near highways and port links shortens linehaul distances and reduces LTL fragmentation. Carrier density improves pricing leverage and routing options, which tightens delivery windows. Assess typical transit times to your top customer ZIPs and the 3PL’s negotiated carrier contracts for predictable freight rates.

Require a WMS with real-time inventory synchronization, API-based order and shipment integrations, EDI or modern webhooks for carriers, and support for slotting, batch picking, and returns workflows. Verify reporting cadence, data accessibility for forecasting, and the provider’s change-management process for integration.

Key cost drivers: storage rate by pallet/CBM and minimums, pick-and-pack labor and transaction fees, inbound receiving and putaway charges, returns handling, and value-added services like kitting. Also factor in fuel surcharges, peak season premiums, and any minimum monthly activity commitments that affect effective unit costs.