Read as many articles on here as you can find about narcissicts to help you figure that out. Also, there is a very good you tube poster who goes into great detail about how to spot them on youtube. I think her name is the illisuion dispeller. Look her up.

If your gut tells you something is off, then it probably is. One thing that you can do is to stop doing what the narcissitic wants, or to stop complimenting them. Once you do this, they no longer have a need for you and they'll move on to their next victim. They need constant validation and they have a constant need for approval.

If they seem fake, then they probably are fake. A genuinely nice person with good intentions can take a little bit of critisicm or hear the word no once in awhile. They don't make everything all about them for example. Also, they care about other people. A narcissitic person will rarely ever ask you about yourself as everything is all about them.