Consignors, those who place their property with you for sale, are vendors, those you pay are vendors.
QB is totally unsuited to be a consignment shop software, it will do the accounting for you but as summary data, not as day to day operations. If you are running an actual consighment store then you need consignment shop software. Several years back I reviewed some so this review is out of date, but it gives you a starting place. http://onsale-apparel.com/Rustler/consignment-shop-software
Item placed with you on consignment are not inventory items, you do not own them.
Hey @slwhig, I think what @Rustler is trying to say is that QuickBooks doesn't work like a POS in the traditional sense, in that you can't easily run variable transactions in and out of it in a high-paced environment. Especially since you are dealing with appraised items that are individually price-dependent, you'd need something more purpose designed.
Then, use QuickBooks to track collected sales at the end of the month for whatever overhead you charge to the seller, any fees you might charge for your services (if you do appraisals), and expenses to your business (rent, insurance, etc). That way, you have one program tracking the day to day transactions (including what was paid and how the money was distributed, etc) and then you port the data you need for the income your business makes from the consignments in QuickBooks at the end of the day/week/month.