Suppliers that ship to Amazon vs sourcing freight shipping

Someone replied to another post of mine alluding to having a Chinese supplier ship directly to Amazon. Shipping quotes out of AliBaba often seem outrageously high, so I imagine the supplier shipping on your behalf to Amazon for you to resell might cost you some bucks… otherwise they’d just sell it themselves. So when does it make more sense to have the supplier ship, versus trying to go through the pain of sourcing a local (in the example Chinese) agent who will freight ship by volume to your local port (I just happen to live in a major port city on the Pacific)?

TIA!