What is the ruling on trading in electronic devices such as satellite dishes, computers, and video players, and is the seller responsible for how the buyer uses them?

The default is that buying and selling are permissible, unless something occurs that makes them unlawful, such as the item being inherently forbidden (like alcohol), or forbidden due to an external factor (like selling weapons to bandits, or selling grapes to someone who will make wine from them).

The first type (inherently forbidden) cannot be sold, bought, or assisted with under any circumstances.

As for the second type (forbidden due to an external factor), the prohibition of selling it is conditioned on knowing that the buyer will use it for unlawful purposes. This falls under cooperating in sin and transgression, which is prohibited.

Islamic law has equated those who cooperate in sin with those who commit it in terms of sin and divine threat. Examples include the curse on alcohol, its drinker, and its seller; and the curse on the one who consumes usury and the one who feeds it to others.

Since some of the items in question are used for unlawful purposes more often than for lawful ones (like satellite dishes and video players), it is not permissible to sell them except to someone known to use them only for lawful purposes. As for computers, their use for lawful purposes is more common or equal, so their sale is permissible unless it is known that the buyer will use them for unlawful purposes.