Well, let's consider what alignment our PHB-possessing friend is. He can't be evil, as most of you folks are, because he was willing to give something of his own to help others. The bookstore might have gotten in trouble for selling the book early, and though the odds might have been slim, BVB was willing to give the book back to protect them. He obviously seems to be edging toward good here.
And he also isn't chaotic. The bookstore asked him to turn the book over because of a regulation or agreement the bookstore was under said that they shouldn't sell the book early. A chaotic person, even a chaotic good one, would probably consider such a rule silly, as most of you folks are claiming. He'd keep the book, because yes, he did pay for it, and it's the bookstore's problem if they messed up.
So BVB is obviously lawful good, willing to sacrifice for the good of the store, and because he doesn't want to disrupt the proper order of things. Sure, there's probably not a law that says BVB would get in trouble, but the bookstore might be liable, and he didn't want to risk that. I commend him.