Well, after you check that all the stitching and hardware looks and feels right, (check the authenticity threads, I think there is specific info on this) then one thing I always do is SMELL the leather!
Chloe's leathers smell delicious! There should not be any odor other than a rich "leathery" one. If there is any chemical, plasticy or strange smell to the leather, it's fake! I have many Chloes so I check "against" the ones that I have and the new one should be identical, inside and out, except of course for the serial tag on the inside pocket which gives the info for when it was manufactured. There are specific things to look for in the locks as well, and again, the authenticity threads are the place to go for this info. I have had GREAT luck with Bluefly!