If my field, I tend to get a fair amount of out-of-the-blue sales calls. I have caller ID on my office phone, so I can usually tell when a call is a sales call, thus don't bother to pick it up.

However, if they call me twice (usually spaced a few days apart) and both times I let their call go to voicemail, then they call me from a cell phone number...which I pick up because those tend to be legitimate calls.

Has anyone else encountered this tactic?