Recently, with the rise of social networks and the influence of Search engines, on several occasions I have had Recruiters/Headhunters say they "found me on LinkedIn" or "found me via Search engines" or some weak response like that, when I ask them how they got my contact info. On one occasions, I kept on probing on how they got my info and where they were from, and they quickly decided to end the phone call.
Being the skeptic, and being aware of the fraud that can be out there, I sometimes question the legitimacy of some of these recruiters. Should I hold off sending a resume until I can validate them? What sort of "innocent" questions can I pose to these recruiters to tell for sure that they are legitimate? What sort of follow up questions should I ask if they say they found me on LinkedIn or other online source to see if they are legit? Should I politely tell them that I'm not interested in such solicitations?