Yes, I agree with you. It is mostly word of mouth. So, do you trust your family and friends to lie under oath to protect you? Even those who would not intentionally turn you in might say something unguarded or stupid when pressed. So it isn't just a matter of trust, it's a matter of whether you believe they can be sufficiently crafty when necessary. Many people are just not that sophisticated.
What good is less than 1%? Not good enough. I would not be able to sleep at night knowing that I might be caught. Only 0% would be good enough, and there are no such odds.