As long as there is a real time shipping method on the order's ship via field, the system will always prompt users to calculate the shipping cost before saving the order. Do the following steps to disable automated shipping costs:
1. Set the Sales Order's Ship Via to blank 2. Setup > Accounting > Shipping > Default Shipping Method=set to null/blank as well.
Note: This is to set a null value on the Sales Order's Ship Via field everytime a sales order is entered