Visit this website: http://www.scamadviser.com/
and enter the URL of the website that you want to check the authenticity of.
Further, you should "google" the website, together with the word scam or do a "is this legit" test on it. I.e. if the website is called www.amosmacdrops.com then just google "www.amosmacdrops.com scam" or "is this legit www.amosmacdrops.com scam" and you will see how it has been rated on other websites.
Hope this helps in checking if a website is genuine or not.