First off, beware of the 1099 that Paypal sends you. These totals INCLUDE the items selling price, the shipping charged, and any tax collected. You must deduct the shipping, tax collected, shipping supplies cost, Paypal fee's, and Ebay fee's to establish your taxable income.
I keep a ledger of items sold with shipping costs. This helps at the end of the year to have your total shipping expense.
Of course, when filing taxes a Schedule 1 Form and Schedule C Form will be required to show Business Income. Best to have a professional do the taxes.