I know COMC has an eBay auction option, but it was added fairly recently and I don’t have any experience with it as a buyer or seller. However, I have sold a few batches of old sport cards through their standard sales approach (similar to eBay’s ‘Buy It Now’ feature). Basically, you mail your cards to COMC and they process the cards and add them to your ‘owner dashboard.’ From your dashboard, you are able to list your cards for sale and set the prices you’d like to receive. When a card sells on COMC, you get an email alert and receive the sales proceeds in the form of store credit. COMC mails the card to the buyer, but typically buyers will wait until they have multiple cards to ship so they can save on shipping costs (buyer pays 100% of shipping), What are the fees? Well, you have to mail your cards to COMC. I’ve found that when I’ve mailed a batch of 100 cards, the shipping charge and cost of materials to ship safely run about $20 (so $0.20 per card). Then COMC charges a processing fee of $0.25 per card to list them on their site (so we’re up to $0.45 per card). COMC also charges a 5% sales commission and an ongoing fee of 1 cent per month per card. So hypothetically, a $2.00 sale would net you about $1.30 after fees (assuming it was listed for sale for about 10 months). I mainly use COMC to build small collections of my favorite 1990s Packers and to speculate (or flip) cards I think are listed for sale below their actual value. I spend about $10/month and it’s a fun, inexpensive hobby. That’s really the extent of my sports card knowledge and I’m sure other, more experienced collectors could weigh in here. I just wanted to mention COMC as an option because my experience has been very good.