Panerai watches are very hard to identify as real or counterfeit. The beauty of these watches resides in their simple look, which doesn’t cause much problem to replica watch factory. Even worst, Panerai is using for the vast majority of their watch, movement from ETA SA Manufacture Horlogère Suisse (ETA SA Swiss Watch Manufacturer) which are easy to buy from anyone nearly everywhere. That makes it so easy to replicate that even the movement look can’t be a sign of if you are about to buy a genuine Panerai or not.
Most of their watch uses an ETA 6497-1 or 6498 movement. As you can see from this comparison, only the overall look change since they are decorating the bridge to their brand.
Basic ETA 6497 / Genuine Panerai watch movement.
But that is not a big work, even apprentice watchmaker can personalize external part of the movement to their liking. So replica factory has no problem to replicate the design Panerai is using.
Fake Panerai movement / Genuine Panerai movement.
Chronograph's models are made from the ETA 7750 or 7753, which are widely used by other brand also. Zenith has also supplied movement to Panerai back then. Even with the more complex movements, Panerai is still use generic movement like the Lemania 2310.
No-name Lemania 2310 movement / Genuine Panerai chronograph movement.
So unless you are looking for a Panerai which use their own in-house movement like the Eight Days or the automatic Cal P. 9000, the best advice to be sure you get the watch you pay for is to get it from a very reputable source. Panerai is a brand which is way too easy to get scammed with fake watches.
Genuine Panerai P. 2002 and P. 9000 which to this date, are not been made by counterfeit watch maker.