You can deduct all shipping costs you paid either shipping to you or that you paid to ship to your customer.
Don't think I understand your #2. If you charge the customer the full amount plus shipping then that is your gross income. You can then enter the total shipping as a separate expense.
#3 The whole shipping amount is an expense. See #2.
Probably would help to use examples with amounts. Say you charge the customer $220. $200 for the item and $20 for shipping. You enter $220 for income. Then you enter the $20 shipping as an expense and the net profit would be the $200. But if the shipping actually cost you $30 you enter the $30 expense. Then your net profit would be $220-30=$190.
