While the usual case is for the consignment dealer to pay for an item after it is sold, sometimes they do purchase the item and resell it themselves.
If this is the case, within the Item Administration command for consignments, you can simply select “Yes” for the “Cash Purchase” dropdown for that item.
The system will know not to additionally deduct a commission for the consignment dealer. Your company’s commission will still be calculated based on the sold amount as usual.