If your first instinct when a strange number calls you is to call back, you might want to slow down a bit. The last thing you should do is call back an unknown number.

More often than not, we think it is a friend, business contact, someone from the job you applied to, or just someone from work calling with a strange number.

But you should always think twice before you pick an unknown call or return it. Here are the most likely reasons why:

1. Wrong number

If you weren’t expecting an important call from someone who promised to call you or if you have not just left your phone number for a callback, then it is most likely someone who mixed up numbers. You would be wasting your time and your money trying to hear the stranger while they rattle on in an incoherent language. This might tick you off and put you in a sour mood for the rest of the day.

2. Someone you don’t want to talk to

“Hello, do you remember me?” Conversations that start like this are probably bad news: an unwanted ex, someone that wants to borrow money, an annoying aunt or someone you are hoping to avoid. Missing the call, in such cases, was a blessing in disguise, so calling them back is just letting the devil win. If it is very important, they will send a text.

3. Marketing call

Your network provider has a new promotion coming up. Your insurance company is doing some sort of offer. Or it is just your bank telling you of some new bank offer that will most likely cost you more of your hard-earned money. You will be saving yourself from getting sweet talked into something that may not benefit you much.