This authentic v. fake comparison is for the JC treasure chest charm. The fake treasure chest charm is actually pretty good, and I would have bet money that it was the authentic one, until I did some research.
Disclaimer: These charms were both bought from ebay.
The first difference in the photo above is seen on the inside of the lid. In my opinion, the authentic charm lid (L) actually looks brassier than the fake. Also on the lid, differences in the script are apparent. The authentic charm has bolder lettering than its fake counterpart, and the banner's shape is not consistent.
Likewise in this photo, the lid appears higher on the fake (R). I measured them, and they are actually the same height. The reason the fake lid seems higher is because the nails/tacks which hold the gold "straps" protrude more. This is especially apparent on the left side of the open lid.
If you haven't noticed yet, the most remarkable alteration observed in this photo is in the treasure area. The crown is set at a completely different angle and direction, and is brighter gold on the fake (R).
The preceding photo shows the variations in the trunk bottoms. The authentic charm (R) has thinner and more even gold edging. The fake edging seems thicker in some areas, especially at the top/front of the trunk.
This photo focuses on the lock differences. The keyhole in the authentic charm (R) is a little wider and more pronounced than on the fake.
In this photo, you can see that the fake (L) charm lid does not open as wide as the authentic lid. However, I am not certain that this effect indicates a lack of authenticity.
The reason I have included this photo is to show how the handles differ. The authentic charm's handles (R) are much shorter than those on the fake charm. Sorry that my authentic charm has damage on the handle shown, as it is distracting.
Below is an even better picture of the handles:
The photo above shows the details of the jewel placements. Aside from the striking crown misplacement on the fake (L), you can observe that the light purple/amethyst jewel is rotated relative to the authentic counterpart.
And, the big pink oval at the front of the chest actually touches the front panel, only in the authentic charm (R). The arrangement of the coins is inconsistent as well.
In sum, if you have to make a snap decision about whether an item is a good deal (e.g. a BIN item for a great price on ebay), look at the crown placement, then the JC lettering on the inside of the trunk.
If the photos don't show the inside, you may not have much to go on, other than the protrusion of the tacks or the keyhole on the lock.
Finally, keep in mind that while there is only one authentic JC style of a specific charm, sadly there may be more than one variation/fake created!