LOL, when the threads all get merged together it becomes clear that I can't resist putting in my two cents when anyone asks about YSL patent (and here I am again)!
The one thing I wanted to point out is that the quilted croc patent is different from the croc embossed patent. The quilted croc patent is a version of the textured calfskin patent which is stitched into a croc pattern. The embossed croc is smooth, glossy lambskin patent with a croc pattern embossed onto it.
Here's a quilted croc patent Downtown (pics are from the Reference Library)...
And here's a croc embossed patent Downtown...
I find both to be weather/stain/spill resistant, but because the croc embossed patent is smooth and made from lambskin, it is more delicate and prone to fingerprints and scratches. I just wanted to point out the difference since it seemed like the two versions were being confused with each other at times.
I just took my white patent muse out of the closet today after months of non-use and to my total surprise, the color around the stitching changed to a pinkish color. I am thinking that the thread they must have used to sew the details on the side might have bled into the white patent. So now the "Y" going down the front of my Muse bag is slightly tinged pink. Not very good...a very obvious discoloration on the bag.
^Sorry about your situation. No, I've never heard of YSL patent leather "chipping." Its VERY soft and flexible. The only reasonable explanation I can think of, if the bag is real, is that perhaps the original owner treated it with some alcohol-based product or something that reacted badly with the patent??? More likely I think its probably fake. You said that even the seller herself admitted that she doubted the authenticity. I'd suggest posting pics in the Authenticate This thread.
YSL patent bags are among the most durable ones I've ever had. I have 4 YSL patents, and I've been killing my Majorele and y-mail wallet for 2 years, and they are still holding on. If you are looking for a durable bag you can wear at any weather, black patent it is. No maintanance required - just don't spill coffee on them too often (I assume eventially it would take its toll)
I would recommend to stay away from light colors - they get color spots easily, which ruines them completely.