Is it permissible to sell goods that can be used for both lawful and unlawful purposes, when it is highly probable that they will be used for unlawful purposes, and what is the Shar'i (Islamic legal) ruling on this matter?

The means take the rulings of the ends. Therefore, whatever leads to the forbidden is forbidden. The scholars have explicitly stated the prohibition of selling grapes to someone who will use them to make wine, because it constitutes aiding in sin, in accordance with the verse: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." Sa'd ibn Abi Waqqas uprooted grapes when he was told that they were only suitable for someone who would press them [for wine]. As for goods that can be used for both lawful and unlawful purposes, the original ruling for them is permissibility, unless it is known that the buyer will use them for unlawful purposes; in that case, selling them to him becomes forbidden.