My chanel is sent for a clasp change

You will lose substantial amount of money if you want to sell it on websites other than ebay. Sites such as Vestiaire Collective charges around 30% commission and they will press your price down to whatever "fair price" they determined.
You can do a quick search on a particular platform for similar items and the price they are listing, deduct 30%, and it will be the price you are going to get.
PS: I highly NOT recommending Vestiaire Collective for selling your items.