Why Louis Vuitton behaves differently to every other house
Louis Vuitton is the one brand where you are buying a future as much as an object. Coated canvas is stable; the vachetta trim on it is not. Untreated leather darkens with sunlight, water and the oils from your hands, and it does so unevenly at first. That is expected behaviour, not a defect, but it surprises people who only ever saw the bag on day one.
The grain is the visual check. Genuine coated canvas has a regular, slightly raised grain with a consistent matte sheen; a poor imitation looks either too flat or too shiny. A single close frame in daylight settles the argument more reliably than any stamp.
Stitch is the second. LV runs a specific stitch count per inch, and it is visible where the handle meets the body. Uneven pitch is not a style choice, and it is the most commonly cited tell in comparison threads for good reason: it is cheap to get wrong.
Written for Louis Vuitton specifically. The same discipline applied to a different house produces a different list - see the brand index.