There is a lot of money being made by unscrupulous dealers who deal in counterfeit items. This is because not everybody can buy designer items as they are so expensive, whereas fakes are much cheaper. Luxury watches are the most counterfeited items available today, and sometimes it is not easy to tell a fake from the real thing.
As in anything, to be able to tell the real thing from a fake you need to be very familiar with the original. In the case of timepieces, familiarize yourself with the brand you have chosen. Make sure that you know the different collections that are available as well as their distinguishing features.
Check carefully to see if there is any glue or glue stains anywhere on the watch. If the logo is stuck on with glue, or there is gluing on the crown, then you know that what you have is not a designer article. This should help you determine the value of the watch you are looking at.
Silence is also one of the hallmarks of luxury timepieces. They are quiet, so if you hear a ticking noise from the second hand, or if you can feel vibrations or hear clicks when you twist the knobs, this should alert you to a possible fake. Not all genuine ones are silent however, which is why you should know the features of the genuine article.
The inside of the clock-face should be clean and dust-free. If there are hairs trapped in the face, or dust in the mechanism then that watch has been manufactured in conditions where checks were lacking, making it a likely counterfeit. Real designer brand chronographs are spotless in all respects.
A common way to recognize fakes is the English used in any marketing or even on the watch itself. There should be no grammatical or spelling errors. The letters should be the same size, and they should be sharp and not blurred. If this is not the case then that is a fake watch.