1099k for selling old clothing

Hello, there is a lot of discussion around this but different answers so I'm more confused now. If I received a 1099-k from ebay/poshmark since I crossed the $600 threshold (crossed it by maybe $10) - how do I write it off so that it is not taxable since Im just selling old textbooks/clothing for less than the original value that I bought it for? I don't have all the receipts since some stuff are years old and I doubt all us casual sellers keep receipts for used clothing. I've heard some advice to either file a Schedule D or Schedule C - which one do I file? Some say to list it as other income on Schedule 1, but I don't that's correct b/c everything on Schedule 1 is taxable. Can someone point me in the right direction?