recently I believe the words of people who I've just met, he said that he could multiply the bitcoin that I have, I was curious and menconya, I gave him 0.02 bitcoin, and in the end he made off bitcoin I have 
High returns, short ROI, unrealistic rewards, high referrals or affiliate rewards and bonus; if someone or in some place you read this kind of offers, they are likely a candidate of a ponzi scheme. Don't just get hooked just because the offer is really interesting. To make people to join in ponzi owners creating a nice intro so hearing some unrealistic return will be presented to their clients.