I'm pretty new to Bitcoin and the idea of cloud mining seems pretty appealing. However I keep hearing about Ponzi schemes which rely entirely on new members to stay alive. Besides the blindingly obvious, what are the main signs that a service might be a Ponzi?
Cloud mining sites are not appealing they are appalling, and the simplest way to know if a site is ponzi is to see if the returns are way better than anything you could get, the website looks unprofessional, there are not phone numbers you can call or a physical address, there are lies in the web page, and there probably more signs to identify a website as a ponzi.
It's good to check if there is a phone and local address, but it's not sufficient. When the investment site show you an address, try to find it on google maps or any other app. The address can be fake and doesn't exist in real life.
HashOcean did it. They had phone number, address, but all fake. The legitimacy of site owners is important too, look if they are reputable persons in Bitcoin businesses area, possible to know it when they are members of BitcoinTalk Forum.