Are you keeping an in inventory? Don’t use line 38. Use line 22 for supplies or line 27a for other expenses.
For self employment income on a schedule C you have to enter the total gross income you received (including the product, parts or reimbursements) and then you enter all your expenses. Reimbursements would be an expense. Product and parts would probably be entered as Supplies. Or you can use line 27a Other Expenses. Then only the Net Profit (or Loss) on Schedule C goes to your 1040 and gets taxed.
