There are so many social networking and online dating websites. It is fine to add a person you know but sometimes you receive requests from people who are unknown to you. It is very important to make sure that the identity of a person you are going to add is not fake. Most people send you requests and impress you with their display pictures or avatar.
Steps to Identify Fake Profiles
1) Go to the suspected profile.
2) Click on the profile picture then click the thumbnail to enlarge it.
3) At this point, the picture is probably inside a transparent Facebook dialog box. You'll need to refresh your browser so the page reloads the picture. Once the page has reloaded, right-click (ctrl-click on a Mac) the picture and select "view image". This will be the actual URL of the image. COPY this URL. (I use Firefox, other browsers may work differently)
Alternatively, you can use Facebook's "download" image link to download the image to your computer. Then you can upload it to Google Image Search.
4) Go to http://images.google.com/
5) In the box where you normally enter what to search for, you'll see a little camera icon at the right. Click it.
6) When you click the camera icon, you'll get the option to PASTE the URL of the suspected photo or UPLOAD it from your computer.
7) Once the search results are displayed, SCROLL DOWN past the "similar" photos to see if the EXACT SAME photo has been found on porn sites, college humor sites, blogs, or other profiles.
I have used this a lot of times and most the times I have seen that people use images which are leaked on some forums. If you identify such profiles then Please report it to Facebook.