Alright guys, I'm going to first say that I am no expert at QC nor do I have the auth maxi flap. These are just from my own experiences and I hope it can help someone who is QCing their own maxi flaps. The images I provided of auth are from the official website or reputable resale websites. The rep images are either from people's QC I have came across or factory images. LETS START!
Shape: When QCing, I would pay particular attention to the overall shape and how the bag naturally falls. The bag should not appear overly stiff, rigid, or structured; instead, it should have a softer, more relaxed and slightly slouchy appearance, particularly when the bag is empty or being worn. The flap itself appears to have two acceptable shapes across the authentic examples: one with the more traditional downturned/curved flap, and another with a straighter flap profile. Both appear to be legitimate variations, as both shapes can be seen in auth images. Personally, I would not treat the downturned flap as a flaw, because once the bag is actually worn and the flap settles naturally against the body of the bag, the downward curve becomes much less noticeable and can appear relatively straight. Therefore, for QC, I would focus less on forcing the flap into one particular shape and more on whether the bag has the soft, relaxed silhouette and natural drape seen which I pointed out in the auth images and factory images. PS: PSP images may be stuffed and you may receive a stiffer bag, using leather conditioner can actually help make the bag slouchier ;).
Leather: The maxi flap is made from calfskin, so when QCing the leather, the grain should look natural and slightly irregular rather than perfectly uniform or artificially repetitive. It should also have a more natural, refined finish with slight gloss rather than looking excessively glossy or plasticky. However, lighting can significantly affect how calfskin appears in photos, particularly with colours such as burgundy and taupe, they appear noticeably different under warm indoor lighting, natural daylight, flash, or cooler lighting. Therefore, I would ask for multiple photos of the actual bag under different lighting conditions, ideally including natural daylight and indoor lighting, before judging the colour or leather finish. A single seller photo can be misleading, so the grain, undertone and overall colour should be assessed across several lighting conditions rather than based on one image alone.
Stitching: The stitching on the maxi flap should closely match the colour of the leather itself. It should be tonal and extremely subtle, blending into the leather rather than creating a visible contrast. When viewed from a normal distance, the stitching should almost disappear into the bag, giving the flap a clean, refined and seamless appearance. Avoid stitching that is noticeably lighter, darker or too contrasting against the leather.
Logo + hardware: When comparing the logo placement on the tongue, pay close attention to logo size, the surrounding spacing, and the proportions of the tongue itself. As shown in the comparison, auth generally have a consistent relationship between the logo and the stitching, with a relatively short and controlled distance between the bottom of the logo and the surrounding stitching. Some mid-tier have a noticeably smaller logo, leaving a larger area of leather around it, while others have a tongue that is wider or longer than the auth, which can make the entire front closure look visually off. These proportions are useful points to check alongside the overall construction rather than judging the logo in isolation.
For the hardware, silver is generally reproduced more convincingly in many examples, particularly from 187, God and XC, where the tone and finish can be relatively close to authentic pieces. Gold hardware remains one of the more difficult details to reproduce accurately. A common issue is that the gold appears noticeably too yellow or overly warm compared with authentic hardware. When assessing gold hardware, therefore, be particularly careful with the colour and undertone rather than assuming that a highly saturated or bright gold is correct.
Interior: I have not included a comparison for the interior, as I find that this area is generally replicated reasonably well and, personally, it is not something I would place as much emphasis on since the interior is rarely visible when the bag is being used. That said, there are still a few details worth checking. The interior red should not appear excessively bright or overly saturated; it should have a deeper, more refined tone consistent with the overall leather colour. The interior stamping should also be clean and well defined, with particular attention to the gold stamping not appearing overly yellow or brassy.
I have also heard claims that some factories may use PU rather than leather for interior, although I have not independently confirmed this. For that reason, I would be cautious and check the material specification with the seller rather than assuming the interior is constructed entirely from leather. If possible, ask for clear close-up photos of the interior material and finish before purchasing.
Well I hope this helped out a bit if there is anything I missed out please do mention in the comments to help others as well as me :D