I run a multi hundred thousand dollar business (not on depop, my own website and etsy) and as the seller, unless the buyer purchases insurance the seller is not responsible for lost mail / incorrect delivery / stolen mail etc.

I do however offer a replacement at a restocking fee and shipping fee out of convenience for items "lost" in post for those who didn't purchase insurance on their shipping but most companies don't even do that. Any refund does not come from my seller account but from Etsy itself in some instances where they will refund but most platforms do not hold the seller accountable so long as it's shipped with tracking (you can check the policies) it sucks, but it is the truth