I saw an advertisement of CryptoX2 recently, and tested out the website. They promise to double deposits within 24 hours. The first time I used it, they paid me fully, and the second time worked too, but I have heard a lot of stories about similar sites being scams, so I am wondering if this is one of them, or if not, how the site works? Does it wait until the amount I deposit gets higher before not returning any money?
It is definitely a scam. They typically pay people who paid in before with the payments of the people who pay in later. This is unsustainable and it will collapse leaving those who paid in later without any money. Furthermore, most of them will simply take your money and leave. This is a scam and so is everything that promises absurd rewards. This includes doublers, HYIPs, ponzi schemes, etc. You pay in at your own risk and if you lose money, then that is all your fault and there is nothing you or anyone else can do to get your money back.
Reductio ad absurdum: Let's say it works. Invest the equivalent of 1$ on Day 0.
- Day 1: you get 2$, let's reinvest them!
- Day 2: you get 4$, let's go on!
- Day 30: you get 1073741824$, i.e. in one month you are billionaire.
- Day 37: you are the richest man in the world
Then why doesn't the creator of this "Bitcoin Doubler" do it for himself? If it works, he should already be the richest man in the world, but he's not. Problem!
If the doubler worked for you, consider yourself lucky.
These types of websites never work long-term; nobody can double money forever.
If you continued to do that, the probability of you losing the money goes to 1; you will certainly lose the money.
These types of frauds are called "Ponzi Schemes", see more information in this wikippedia article.