I'll have a full post on the 2013 Mike Schmidt cards I've acquired this year, but this card started me speculating about eBay economics.
2013 Topps Allen & Ginter Mini A and G Back #143 Mike Schmidt
The seller sent it in a regular white envelope by first class postage. The actual postage was $0.66. So that leaves $0.35 for the seller. The card must have cost him something. I bought a hobby box of Allen and Ginter on eBay for $0.45/card, presumably he paid less than this. Lets say he was able to get the card somehow for 20 cents. That leaves 15 cents profit. eBay gets some of that.
The envelope cost something, although he didn't spend much on packaging. The card was in a penny sleeve with an old 1988 Leaf card for backing. He taped this to a piece of random cardboard, cut to fit the envelope.
The envelope has a postage sticker from a post office some 30 minutes away from where he lives. Hopefully he didn't make a special trip just for this card. The seller has 15 feedbacks on eBay so he's not a volume dealer.
I've sold some stuff on eBay but it's been years. One of the reasons I stopped was that it hardly seemed worth the effort.