Ten years ago, when I worked at a large investment company, management hired 25-year ex-CIA and FBI veterans to teach me how to tell when a CEO is lying to us. This helped me tremendously to avoid investing in companies that had misleading or unethical CEOs.

The former CIA and FBI employees who taught me were sharp and personable, and they actually made the whole exercise a lot of fun. They showed me many videos of CEOs and taught me how to look for body language indicating that the CEO is most likely not telling the truth. Since then, I can almost always spot when a CEO or executive is lying in a television or in-person interview.

Here are four things liars often do.

1. They have long-winded answers to simple yes-or-no questions.

If a business contact of yours rambles on and on when answering a relatively straight-forward question, then there is a high probability that this contact is lying to you. You need to make sure that the person you are speaking to doesn't usually ramble on and on in conversations with you. If he or she rambles when answering a simplistic question, the odds are they are not telling the truth.

2. They often don't make eye contact when answering a question.

If a business contact breaks eye contact when answering a question, then there is an extremely high probability that this person is lying to you. Try asking someone selling you a product if he or she has disclosed all of the most important risks to you. If the seller break eye contact for literally a fraction of a second, they are probably lying to you (unless this is their normal demeanor).

3. They put their hand on their mouth when answering a question.

This one works exceptionally well. If you notice that the person you are speaking with does not usually cover his or her mouth but does so when answering your question, the odds are this person is not being fully transparent.

4. They shake their foot when answering a question.

People often get very nervous when they are lying, which is what a lie detector machine senses. If you see someone who is seated moving/shaking his or her foot, the odds are you are being lied to (unless he or she drank too much coffee).

If you witness one of the aforementioned clues in a conversation, ask additional questions. If you then see a second or third of the aforementioned behaviors, then there is an extremely high probability that you should never do business with this person.