Vinted complaint: Fraud and no refund

I have two similar complaint
Complain1: I bought a dress from a seller for 50pounds , the dress came smelling and with some makeup stains and loose threads . I couldn’t even try on the dress because of the smells I returned it . The seller claimed I did the makeup stain and vinted let her keep my money and the dress.
Complain 2: I sold a jumpsuit and the buyer didn’t like it, I asked her to return it and I will refund her money. Before I returned the jumpsuit vinted refunded her . Now she is refusing to return the jumpsuit she said she has binned it . how is that fair ..How do i loose both my item and money bought as a seller and as buyer . As a buyer , I actually paid buyer insurance and still i get reaped off . Why I’m i not protected by the buyers insurance ?This is fraud ! I think they are committing fraud or conspiring with some sellers .