Is there a specific reason you want to check if a company is fake? Please describe your need for doing so.
No one knows whether a company is fake or not unless you verify it yourself. The first instinct when checking a company is to identify the type of business they run by speaking to the employees working there to gather comprehensive information. Make sure to verify that their web address is correct. If it exists, take note of their contact information from the site and call them as if you were a candidate applying for a similar position to gather accurate information.
You need to provide more details for us to understand your current situation so that other forum members can respond appropriately.