“What are my legal obligations here? Do I have to send the book back if I never agreed to receive it in the first place? I don’t really care whether I get to keep the book or not but I don’t want to be constantly receiving this junk and having to spend the time to return it. I figure if they don’t get the first one back they might get the message that no means no. What say you?

PS My state of resident is Kentucky”

What you describe is not terribly different from the kinds of “book club” and “record club” schemes that have been around for decades. They get you to sign up and then keep sending you unwanted products. If you are certain that you did not agree to buy a certain number of books from them, then you are under no obligation to accept them or pay for them. But you can’t keep them.

One strategy is that when they are delivered, tell your mail carrier that you wish to “refuse” delivery. (If you don’t catch your mail carrier, you may need to take it, unopened, back to the post office.) They will return it to the sender with postage due by the sender. After being charged for the post office, most mailers will quickly take you off their list.