The leather holds up beautifully, actually! The creasing doesn't happen where it opens on the sides, but rather on the leather tabs that holds the strap on both sides. So, you would expect the bag to slightly curve inwards where the leather straps are held onto the bag, since the weight of the bag is constantly pulling on that area. Just looking at the listings on Fashionphile, I identified the problem with most of the pre-loved Saintonges. Here's an illustration, if it helps:
View attachment 4446517
Not obvious and doesn't cause any usage problems, and mine only did that after wearing the bag consistently for 3 months nonstop during summer, never changing out of it! Otherwise the leather looked absolutely amazing and only very light scratches, not very visible at all. Really help up very well against all weather, easy to use and matched everything, would recommend.