I'd like to fix up the analogy a bit. The problem isn't that you're asking for a random ISBN numbers; it's that you don't have a library card. The library's electronic catalog won't let you log in without the card, so you just start asking the librarian for random ISBNs and accepting the books he gives you. He doesn't check on your card because no one trained him to do that, but you know that checking out books is meant for card-carrying library members. I sense deceit there.