When you start to collect watches sooner or later you come across examples that are not all that they appear to be. Some of these will be fakes and some will be part of the burgeoning market of homage watches. It is a good idea to spend a little time explaining the two, how they differ and what to avoid.
Fakes & Frauds
Fake watches are copies of mainstream watches with lesser value parts, these are presented to a purchaser with the hope that they will part with more money than the watch is really worth. This is often accomplished by selling a high value fake watch at a low (but still far higher cost that the sum of its parts) price so the buyer feels they have got a bargain and must buy it.
I do not currently have the expertise to detect a fake at 5o yards but I can offer the tried and tested advice in this area. If you are buying online only purchase from reputable dealers (be that on eBay or elsewhere), do not buy from recently established sellers without a proven track history. Do your research, if you are looking for a particular brand of watch, search watch forums about how to spot common fakes within that brand. And the old tip, if a deal looks too good to be true, it probably is.
Homages & Sincere Flattery
Homage watches are a little more complex and less exploitative (if the sellers are upfront about it) , there is a range of fake (or homage) watches that take direct design clues from famous brand luxury watches. These are often sold with alternative dial mark branding or unbranded, they are presented as homages to the original and are sold as such with no claims to contain the movements or complication of the original. This is one way people can obtain a luxury brand watch at a fraction of the cost, albeit a look alike with different branding, movement, reliability and history.
These are frequently manufactured in China and vary in quality between sellers, however if you are prepared to do some research and find some reputable sellers, good quality homage watches can be found with a reasonable price range. I can recommend a thread to read on this from watchuseek, about Parnis one of the more well know manufactures of homage watches.