In order to authenticate a Kelly bag from Hermès, it is important to analyse a number of aspects of the bag. 

First of all, the shape of the Kelly should be taken into account. The authentic Kelly bag has a very recognisable structure and proportions as well as exceptional craftsmanship. 

After that, it is necessary to examine the quality of the leather, stitching, details, engravings, stamp, code, handle, strap, lock, and keys.

What is worth paying attention to while analysing the product is the stitching. 

Since Hermès employs hand-stitching at the highest level, if the stitching looks like machine stitching, i.e. it is irregular, has loose threads, or is badly aligned, it means that you are dealing with a fake product. 

The hardware should also be free of defects. In addition, logo stamps should not be deep and should be loyally placed.

It is important to note that the flap, closure, and any other aspects of a Kelly bag should be examined as well.