Originally Posted by
Hyacinth 
There's no easy way to authenticate
any Coach items. With keychains, if you don't own the actual keychain or have a library of very good photos, please ask here for advice. And always ask here before reporting an item to Ebay as fake.
Also please keep in mind that there are a
lot of details we use to spot fakes that we never post in a public forum. The best thing is to let us take a look.
Usually having an incorrect serial number will prove that a bag is fake, and we post numbers so buyers can learn to spot some of the most commonly used fake numbers. But there's a lot more involved in authenticating an item - proving that it's genuine - than there is in proving that it's fake.
But a good place to get a feel for genuine Coach keychains is by getting familiar with the Coach Reference Library forum under the main Coach section. There are several threads with good clear photos of quite a few different Coach keychains.
http://forum.purseblog.com/coach-reference-library/