Inventory shipments

What requirements do shipments of inventory need to meet?
How do I clear customs when I’m sending inventory to the warehouse in Riga or Barcelona?
How should I pack my inventory shipment to Printful's warehouse?
Can I drop off my inventory at your warehouse by myself?
Do I have to ship my inventory to you personally?
Can I send different products in one shipment?
Does Printful ensure the safety of my warehoused items?
Who is responsible for shipments during transit?
Who has to clear customs when I’m sending inventory to the warehouses in the US?
How can I get my inventory returned to me?