Posh is mainly app-centered. You have to do everything on mobile. The only thing I can do on desktop is share during their "parties" and purchase things. Everything else you'll have to do on your phone. I wouldn't recommend Posh for high-end designer items. I mainly sell relatively cheap things (i.e. old clothes that I need to get rid of) and those seem to move well without having to deal with low-ballers. The low ballers only come after designer items- where they want your 4k handbag but in return will trade you for their
Coach handbags etc... (not that I have anything against Coach, but that's the type of trade value or 'negotiation' you should expect from Posh).