How many different ways are there to check that a company online is 100% genuine?

If the site has a forum, you may get an idea if the site is legitimate by reading their forum.

Thank you for all the good feedback @faii which would you say is the best Forum to join?

Who is who data base....

thanks for this awesome information

you can check the data in the website of that country (like : MCA in INDIA)
you will get the full detail of company and also u can go to yahoo ans, google etc

In this case, Google is your friend. Also, you should always be an active member of many different relevant forums. If the site is a scam, you can bet someone out there has already complained

Just can check in search engine and domain registration or can check it in whois.com and now about the information of the site.

You can search in google also yahoo and ask answer websites to discuss and come to a conclusion.