And there would never be any legit ones. All these bitcoin doublers are too good to be true. If you were given some magical method to double your money, why would you even share it to others or use other people's money when you can use yours. Simply telling someone that you have a method that doubles money might put your method at risk, because that particular someone can abuse it or destroy it.

The only way your money can get doubled, in my opinion, is when you started a business and then your product/service has become a social trend. People would surely go in and out of your shop and your profit would just grow exponentially. But even that will not last for years since the hype of your product will eventually end.