I've done well with modern cards consigning to PCsportscards on eBay. From the time I ship to them to the time I'm paid it's averaged about 3 weeks. Their fee structure is straightforward, they run weekly auctions, and tracking your consignments is easy. With most BPs well North of 20% now, I'm a believer that unless the item is truly unique and 5-figures plus now it is smarter financially to move items in local sales or eBay (with or without consignment.) I've consigned a handful of low to mid four figure cards to PCsportscards over the past 3-4 years and been pleased every time.
https://www.pcsportscards.com/consignment