Identify scam sites by looking for informations about it. If it's a cloud mining, they must show real pictures of their farm, not Google Images pictures. If it's an investment site paying dividends, they must show with logic how the money is generated and if it's sustainable. Avoid sites paying high daily interest, they usually appear from nothing, last few days or weeks, disappear and appear again with another name (but the owner is probably the same).

If you have any doubt about a site in particular, ask on this forum or search for a thread about the site on the search box above.