The eBay earnings plus any earnings you made on your own without eBay would be the income, then deduct amid the various categories on the Schedule such as Automotive, Cost of Goods Sold, etc. Your Business Activity would be "Internet Auctions." Be wary of "Office Expenses" deduction as it is essentially a trap unless you invite the public into your office (or home) to conduct sales.

I have been doing this for years without problem.