I saw this first hand, actually it was when I was hired back in 1993. I was an intern, and the boss wanted to hire me, but he told me he was legally obligated to advertise for the position anyway.
He placed an ad in the local newspaper. It kept me on my toes for a month, but my supervisor told me not to worry about it. That's why the newspaper classified employment ads are a complete waste of time.
Serious employers will advertise in more than just the newspaper, they will advertise on college campuses for internships, where there's no shortage of cheap or free labor.
With the Internet it's easy to research whether or not an employer is serious. Check the online job boards to see if the same advertisements are present. You will find that most of them are not present.
The employment classified section of the newspaper is most frequently used as cheap advertising if not used for the obligatory job ad for whom an employer already has someone in mind.