Please see this answer from PatriciaV:
Yes, you may categorize the consignment payments as "Commissions Expense" under Business Expenses.
In general, Inventory accounts for goods available for sale that have an associated cost to manufacture or acquire. If you do not pay for the consigned inventory in your store, it has no associated cost. For this reason, you would not include consigned inventory on your business return. (See IRS Rules here.)
To make things easy on yourself, you can avoid the inventory question all together.
If you use cash method and your total average income for the last 3 years was less than $1,000,000 per year, you don't need to use the cost of goods sold section at all.
Instead, you can just write off your merchandise under supplies or miscellaneous expenses when you purchase it. In this case, your merchandise purchase in 2019 would be fully written off then as a business expense.
