In response to customer requests InventoryLab added an estimated shipping calculation into the Listing screen. This calculation is not recorded and saved into your buy cost. It is only present to help you determine pricing based on net profit as you list.
Actual inbound shipping charges cannot be determined during List. The charges are determined after the shipment is sent and the costs are recording under Accounting>Inbound Shipping. Allowing the entry of them into the buy cost in this field would create duplicate capture of the expense.