How do you know if a love binding spell is working?

Love binding spells don't actually work. And you don't have to take my word for it, either. Perform the following thought experiment:

1. Such "Love Binding Spells" are freely available to anyone with net or library access. That is to say - everyone.

2. Teen heartthrob Justin Bieber is being deluged by millions of fan letters and emails from girls from 12 to 82 each day.

3. All those girls have access to "Love Binding Spells".

4. Yet Justin Bieber has not ran off with any of them. They can't all have done the spell wrong.

There. Through the "magic" of logic, one can know that such spells do not work.