What is the ruling on trading and selling women's adornments to those whom the seller expects will use them to display themselves immodestly to unrelated men in the streets?

It is not permissible to sell them if the merchant knows that the buyer will use them for what Allah has forbidden, because that involves cooperation in sin and aggression. However, if he knows that the buyer will wear them to adorn herself for her husband, or if he knows nothing at all, then it is permissible for him to trade in them.