Well no, if they were on Mars you would need to pay a heck of a lot more for shipping

There are legitimate companies in China, and these days it can be set up so that you don't even know the product was shipped from China. Here is how it works, the seller in Chinay, fills in a waybill that appears as domestic for the United States, they load all the shipments on a skid and ship that skid to the logistics carrier along with a manifest of what the items are, how many and the value for customs. The carrier loads the skid into a container (or a trailer) along with a whole bunch of other stuff, from other shippers, adding all the manifests together. The container is then shipped to the receiving country as a single shipment, destined to a domestic carrier, that means a single brokerage fee and single customs is assessed. The logistics carrier pays the customs, and bills it back to the initial shipper, depending on how much of that customs belongs to their items. The domestic carrier, then opens the container, removes all of the skids, breaks down the skids and sends the items on to the final customer.

If the item is returned, it's returned to the logistics carrier, who will bundle up all those returns destined for the originating country, and then return them there, where they will be handed to a domestic carrier to return them to the original shipper. Nearly every large International carrier, has a logistics arm UPS does, DHL does, FedEx does, and I think TNT does.

Now the Chinese company sets up an account with a US bank, what the bank does is they receive money from customers, and after subtracting a service charge, forward the money to China. The Chinese company could also be a trading company where they ship Chinese goods to the US and US goods to China.