How do ebay sellers afford cheap or free shipping on low value books?

I sell comics and a standard Gemini mailer with one comic costs about $6 to ship Ground Advantage anywhere in the US with the ebay discounted shipping. This means that if I'm selling a $2 book and passing on all of discounted shipping, it would still cost my buyer $8. But I see lots of listings for $2 or whatever that are only charging $3 for Ground Advantage, which ends up being close to half my price.

Even if they got the books for free, they're still losing money on every sale, and when I check their stores they often have mostly low value items so if they're making it up on high value items they're sure eating a lot of losses to get there. I can't compete with that and I don't understand how they can afford it. And to clarify, they're not using Media Mail and you can't really get a package smaller than a Gemini.