DM: It's a strange thing, but giveaways can help sales of physical books. (victoriamixon.com)
The real money in comics wasn't sales of the physical books, it was licensing of the characters for TV, films, and toys. (loudpoet.com)
In addition to income taxes on book revenues and profits, in many states you'll also need to collect and report sales taxes on direct sales of physical books to customers. (toughnickel.com)