Is selling accessories and handbags forbidden if the majority of girls display them as adornment? Is the seller sinful for that? And will he be held accountable for the buyers' misuse of them?

The basic ruling for selling these items is permissibility, just like the ruling for selling anything that can be used for either a permissible or a forbidden purpose. However, if you know that a specific woman will use these items in a forbidden way, then it is prohibited to sell them to her. Furthermore, some of these accessories have no connection to ostentatious display (tabarruj).