Ebay sales by an individual

I have made some eBay sales this year, that exceed the $600.00 limit, sales will total about $1000.00-$1500.00.  All the sales are used items and sold at a loss.  Unfortunately I do not have all the past purchase receipts.  How do I include this on my taxes and ensure I do not pay taxes on items I sold as a loss?

Thank you!