Get your taxes done using TurboTax

The 1099-K is showing the gross payment(s). !099-Ks (from eBay) do not show adjustments, refunds or reversals. I think that is pretty standard. If I put the refund amount (same as net proceed) into expense to net zero those two item(s), what do I put in as the "cost"? What I actually paid for them? I don't think it can be left blank.