Q1: A Ponzi Scheme works if and only if the schemer acts as if they are trustworthy and reliable. Once the con man has a person trusting him, he will persuade them to invest in him. After this, the schemer can use his investor's money to keep his con going.
Q2: The reason why Bernie Madoff was able to keep his scheme going on so long was mostly due to the fact that he was paying his old investors with the money from his new investors. This allowed for no one to expect anything was wrong, therefore the scheme was able to progress.
Q3: A Ponzi Schemer is usually the type of person that you would tell a secret to, he/she seems to be a very trustworthy person and will most likely persuade you to invest in him. A con man could also be described as being very charming (even if you just met the person, you would feel like you've known them your whole life), this contributes to the reason why you end up trusting the Con man and investing.