They are friendly and may take a personal interest in you and your life. They call back to tell you positive things about the investment they're offering. Scam operators do everything in their power to make a sale. Often, once you have paid up, contact dwindles, and then stops altogether. If you can't get answers to your questions this may signal danger.
Every investment involves some risk.
Be especially careful if the salesperson downplays any downside or denies that risk exists. Check your comfort level with any financial proposal. If a risk is going to keep you awake at night - don't even consider it.