Rolex, a Swiss watch company, is the leading producer of luxury watches in the world. Many people buy Rolex watches over the Internet without seeing the watch first. Well made, fake Rolex watches can be expensive and are nearly identical to a real Rolex. Because there is a large counterfeit Rolex market, you should make sure that the Rolex you purchased is authentic.
Turn the watch face down to inspect the back of the watch. Some Rolex replicas have clear case backs that show the inside of the watch, but authentic Rolex watches never have clear case backs. Authentic Rolex watches also never have engraving on the case back. When an authentic Rolex is first shipped to you, it will have a hologram sticker on the case back. The hologram will have a Rolex crown above the watch's reference number. Many replica watches will have a sticker, but it will not be the correct design or have a 3D hologram.
Inspect the magnification level of the crystal above the date on a Rolex. On an authentic Rolex, the magnification will be 2.5 times, whereas it will only be 1.5 times at most on a fake Rolex.
Unscrew the crown by turning it counterclockwise. If you have a Submariner, Sea Dweller or a Daytona, you will have a Triplock crown, which is a rubber gasket at the base of the crown. When the crown has popped out and is in the "neutral" position, you can see a black rubber gasket between the crown and the watch. A Rolex replica will probably not have this Triplock feature.
Hold a magnifying glass over the 6 o'clock position and look for the etched Rolex crown on the crystal. Beginning in 2002, Rolex started etching a crown into the crystal below the "6." By the end of 2003 to 2004, all Rolex watches have the crown etching. The etching on a replica, if there is an etching, will not have the same features as an authentic Rolex etching. See Resources for a picture of a replica and authentic etching.
Remove the bracelet on both or either end of the case. This can be done by a professional if you do not have a tool for removing the spring bars. The reference and serial numbers are engraved between the lugs on the watch case. On a replica Rolex, the number is "acid etched."
You can take your Rolex to a jeweller to examine the movement. By opening the case, a watch worker can tell if it is a genuine Rolex movement.