• If you don’t recognize a number, don’t call’em back.
• If you really want to call back, Google the number first. Check the area code to make sure it’s not long-distance. Check the full number, too; in many cases, you’ll find a page full of results saying “Do not call! It’s a scam!”
• If you’re an Android fan, try to get on a device running Android 4.4 (KitKat). It has a built-in number identification system, and it works quite well for at least identifying legitimate, non-scammy phone numbers as safe to call.
• Check your phone bill for sketchy charges. Your carrier knows aaaall about scams like this, and will generally reverse the charge if you complain.