I collect Rolex's and Breitlings...and you can definitely tell the difference between a real and a fake ! If you aren't familiar with what you are looking for, just take it a reputable jeweler who sells Rolex's..they can usually check the serial #'s on a real Rolex and see if it's real. Also, Rolex watches normally have their model and serial numbers on the ouside side of the case, between the lugs where the bracelet or strap attach. You can even call Rolex yourself directly and have them check for you.
New York City / US HQ & Service Center (212) 758-7700
Dallas Service Center (241) 871-0500
Los Angeles Service Center (310) 271-6200
Hope that settles it !