Go to the Collector's forum here on the DIS - there are MANY threads about eBay counterfeits, bad eBay sellers, etc. There is also a site called PinPics where you can see photos of the pins. They have discussion boards as well, and in their forums they have a specific area for counterfeits and scrappers.
The most common justification I hear for buying counterfeit pins is "They look just as good as the authentic ones!" That is an asinine way to look at it.

What would be the point of making a counterfeit that looks bad? OF COURSE the fake ones look like the real ones. Counterfeit money looks real, too. Maybe we should all print some off real quick before we go to WDW!
If authentic pins are too costly then maybe pin trading isn't the best hobby. It IS expensive. And I get REALLY angry when I get a fake pin from a Cast Member that some guest bought from eBay. The CMs can't keep up with all the pins, and it isn't their job to police for authenticity. We buy our trader pins from the
Disney Store or Disney Shopping, so we can be certain that the pins we trade off are genuine.