Dude gets a book for free, vendor pays out-of-pocket to ship merchandise he oesn't get paid for, and vendor's reward is snarky comments on social media because he had the temerity to complain about the situation.

And the book ends up on the shelf next to some expensive new hardbacks. Gotta get that $6.16 back from the used sellers so it can be spent on the worst deal in publishing, meant for those buyers who don't mind spending money unneccessarily.