Selling trading cards at a loss

I played Magic the Gathering for several years and quit a few years back.  I recently needed to renovate my bathroom and sold my collection to a vender for slightly under 15k. Since I sold to a vender they bought my cards at roughly 50% value on the cards.  I still have my recipes from over the years showing that I paid more for the cards than what I sold them for.  I received a 1099-k for what was sold.  How do I report the sale of these cards and since I can prove that I sold these cards for less than what I paid, can I deduct what I paid for these cards as a loss?

Thank you.