Selling items on e-bay is a business to a certain extent. You would go to the Self-employment section, enter in the type of industry and and answer the questions. You do not have to enter in the 1099-K. When they ask the type of income you had, select other, type the word "checks" and add up all of your sales (should match the 1099-K).Then there will be an opportunity to enter any expenses including the cost of good sold (amount you paid).
Here is a link with a few additional steps. entering self employment income
