The best practice for handbag authentication, in my opinion, is not to check strictly against construction details such as number of stitches, depth of heat stamp, or orientation of a Phillips screw, but to trace the use of materials, because manufacturing standard may vary by factory but the selection of materials stays relatively consistent. For that reason, it is always helpful to authenticate a Louis Vuitton by focusing on the Vachetta leather trim and the hardware.
Vachetta Leather Trim
Many iconic Louis Vuitton shapes such as Speedy, Neverfull, Keepall and Noé use a particular type of untreated, fine cowhide -"Vachetta leather" as its leather trim. However, "Vachetta leather" does not simply mean the leather hasn't undergone any finishing such as tanning, painting or coating. In fact, Louis Vuitton has been using highly selected cowhide that does not display any blemish or color variation (think about pure perfection of skin) and this fact alone makes it almost impossible to knock-off the "Vachetta leather". It's just too costly to imitate. In addition, the natural, untreated leather is extremely vulnerable to exterior environment, it will change color through contact of the air, sweat, or grease, a process commonly referred to as "patina". Humidity, stains, human contact will leave their unique marks onto the leather. In images 1 to 3, you can see different stages of patina as affected by its contacts. Some sophisticatedly made Louis Vuitton replicas try to imitate the "patina" using treated leather, which makes it very easy to spot out.
But what if the bag does not use Vachetta? It will actually make authentication more difficult especially if it's Epi or Vernis Leather. Other materials such as Suhali, Empreinte, Mahina are hard to replicate well but because Epi and Vernis tend to have heavier finishing and coating, it's easier to disguise. In this article, you will see a close up on a counterfeit Vernis Alma bag.
Hardware
Based on my observation, the hardware used in making a Louis Vuitton bag has varied very little since 1980's. Brass is the most commonly used hardware throughout history and only in recent decades, more and more gold tone hardware is used especially in higher priced items. According to owner of Cordwainers, Richard Ponce, a luxury leather goods expert, Louis Vuitton has been using unbranded "Riri" zipper for more than three decades, and even on bags made in the 1980's, where the zipper pull read "Swiss", they are from "Riri" too. My personal observation is Louis Vuitton also uses unbranded YKK in older era as well as modern days. Images 4 and 5 show the most common brass hardware used by Louis Vuitton. It's worth mentioning that a Louis Vuitton handbag can have two types of hardware co-existing. In Image 6, you can see brass and gold tone hardware is used in constructing a Damier Azur Neverfull handbag.