How do you know when its a potential employer calling and not a sales call? Answer: you don't. I never answer calls from numbers I don't recognize or aren't already in my contacts list. If its a potential employer calling, they'll leave a message. If they don't leave a message than it was most probably a sales call. By the way, every time I applied for a job on Craig's list, my phone would start ringing itself stupid and every time I answered it was ALWAYS a sales call, so like I said, I now let calls from unknown numbers ring through to VM. To date, no one has left a single message.