It's most likely the proxy bids needed to beat other bidders.
And if we're counting digital and roms, HA. GoodNES 3.23 has 22041 known Nintendo Famicom/NES ROMS (V3.23) When you add all the other consoles, and then move to old PCs, that's a huge amount of digital games you can have. Basically, every game, ever, except old discrete ones with no roms.
Edit: Wait, seller is good deal games? I didn't know this.