On the fake below, the printing of the date is the most obvious flaw. The lines on both numbers are the same thickness as the 4, while the original has a more rounded line with a line at the end of the 2. The start of the fake's 2 is thicker. Note that everything is uniform.
On the real watch, the Rolex font is thicker than the Oyster Perpetual, while on the replica, the letters are more even in thickness. Additionally, the 6 at the top of the dial is more rounded on the authentic model. You can practice checking the authenticity of your watch by looking for other flaws, the above list is not exhaustive.
The cheapest models from brands like Rolex, Audemars Piguet or Omega already cost thousands of euros and even increase in value over time. A brand of this stature would not leave the slightest flaw on a new watch or even an old one as it would damage their reputation. To identify whether a watch is genuine or fake, you just need to pay attention to certain details about each important part of the watch.
Therefore, you can check the authenticity of replica watches by looking for flaws on the index, which is another way of indicating the time, bracelet, hands, buckle, case, or any other element of the watch. On low-quality fake watches, you will definitely see rough cuts and slightly different colors or proportions compared to the original.
It is also possible that the watch is genuine but the components listed above have been replaced with fake parts, so pay close attention to the appearance of each component individually.
Here we can see that the proportions of the borders are not respected. The fake's surface is completely round, while the authentic's is more subtle.
Final advice: trust your gut. If you've acquired a luxury watch in a strange way, or if at first glance you think you're in trouble, it's worth confirming your hunch.