There is really no sure-fire way to identify a fake pin...some of the more common things to look for are mis-spellings and weird coloring.
This is from my longer post about pin trading:
Scrappers, Counterfeits, and Fakes: The second issue is scrappers, counterfeits, and fakes. For some folks this matters, for others it does not. You'll need to decide which camp you are in before you get heavily into pin trading. To the average pin trader, I don't think the difference between a scraper, fake, or counterfeit really matters (because none of these are legitimate pins), but there are slight differences.
- A scrapper is a pin that looks legitimate, but is not. It can be a factory overrun (i.e., the factory was contracted to make 1 million, but they made 1.1 million instead) or a pin that has some kind of error that should have been "scrapped".
- A counterfeit pin is a copy of legitimate pin made by someone that was not authorized by Disney.
- A fake is a pin design that was never authorized by Disney.
Unfortunately, it's not always easy to tell what pin designs are fake unless you know a lot about pins and what designs have been released. These pins can often look like legitimate designs and may contain all of the markings (e.g., copy right) to look legitimate, but they are not. Luckily, I tend to think that outright fakes are the least common type of non-legitimate pins out there.
In terms of the scrapers/counterfeits, those are harder to distinguish the legitimate from non-legitimate. You'll often be able to tell a scrapper/counterfeit because the colors are weird/off, elements are missing or incorrect, or the back stamp (the copy right) is wrong/missing/damaged. Others say you can tell because they feel "rough" or the edges are sharp/pronounced. Sadly, there is no sure fire way to tell a scrapper/counterfeit. My guess is that its easier to identify the counterfeits and the scrappers that should have been scrapped. The factory over-runs probably look exactly like the ones shipped to Disney, so those are nearly impossible to distinguish once theyre in circulation.
It's worth noting that if you do end up trading with CM, the CM lanyards tend to be filled with scrappers, counterfeits, and (to a less extent) fakes. So if you really dislike scrappers/counterfeit, I would avoid trading with CMs. That's the crux of the argument: those that dislike scrappers/counterfeits feel they cheapen the trading and make it not worthwhile. Those that don't care, tend to say that they like the pin, so it doesn't really matter if it's a scrapper/counterfeit or not (they also say that if you can't tell, does it really matter?). Both points are valid.