Also, beware of "Frankenstein" replicas. Many high end replicas, especially of older Omegas like the original Seamaster 300, may in fact use a mixture of both genuine and replica parts.
I've seen some using replica cases, but original dials, and alternate (but still genuine) Omega movements. Those are very easy to mistake for the real thing, so as always if you are in doubt, bring it to a professional.
I know we should not discuss fake watches but there's one thing that still puzzles me. Producing fake watches is not done in a garden shed but done in factories with tooling and design capabilities. Some must churn out watches by the tens of thousands.
Placing a helium escape valve in the right position is just as easy or difficult as placing it in the wrong position. Being in the counterfeit business must be profitable so buying the real deal, dissecting it and copying it exact seems logical. And yet it is seldom done. The result is shown in the above examples. So why don't they do this? Why keep producing flawed fakes? This has always left me clue-less.