You should not mix business and hobby sales.
Business sales are reported as self-employment income and hobby sales are reported as hobby income.
As champ @Critter-3 says, outgoing freight costs would be included as cost of goods sold in the inventory section of your business.
For hobby income, you can no longer deduct hobby expenses on your federal return so you would not be able to deduct the cost of return shipping. TurboTax includes boxes for hobby income and expenses. TurboTax will carry hobby deductions to your state return in cases where you state allows for deductions.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
