Hi Ladies,
I found this thread by chance and am so shocked by all the negative experiences you've had with Vestiaire Collective. They are indeed very popular in France and I have considered selling through them but got turned off by their commission and the way they "suggest" the selling price for your item.
In the end, I decided to work with their closest competitor, Videdressing.com and so far (one year or so later) had pleasant experiences as a "seller". They are not as glamorized as VC but they are doing a fine job. They are improving their site, system and service continuously.
They have, however, increased their commission of 10% with an additional 3 euros per item which, I think, is still reasonable.
Hope this feedback helps!
Thank you for the info, I've not had a good experiences with VC, I will try Videdressing.com