I think it's not worth it. You can end up with an accurate fake easily. While we can do our best to authenticate from photos here, we cannot guarantee that the bag that you receive is authentic, especially when it comes to the Lady Dior and Diorissimo bag.
You also get a warranty for a boutique purchase, and a much better selection of colours.
For preloved, I would recommend that you go to the boutique and feel the leather on the LD first. If you do end up buying it, make sure to thoroughly feel the leather and try to compare it to the one you felt in the boutique. The superfakes that I have seen tend to have a rougher feel (poor dyed job causing the leather to dry out more or simply a low grade leather piece). Fakes have been getting good at replicating the stamps and charms, but the quality of the leathers on the bags are always lacking.
Thank you so much AverageJoe and ThisVNchick for your help; I think I have decided to probably return this one and get a fresh colored one from the boutique.

The price point wasn't that far from the boutique one, pricey pricey.