Most scams are from bitcoin or crypto doublers, those are kinds of "HYIP" sites or get-rich-quick schemes that lures newbies or unaware people who really wants to earn bitcoins so badly. It also comes in form of Cloud Mining, Faucets or other some "other" sites that ends in .xyz,.io,.yz.

Take note: Not all cloud mining sites or faucets are scams. And be sure to check the contents of the sites like its Contact Us or About Us pages and maybe check those scam verifiers on the internet so you can be sure on what risks you'll take.