Would a merchant be sinful if he sold an electronic device (a car Bluetooth adapter) and this device was then used in a way that displeases Allah Almighty?

There is no objection to trading in these devices. Selling something that can be used for unlawful purposes is not absolutely prohibited. Rather, it is prohibited only if the seller knows that the buyer will use it for unlawful purposes. If the seller does not know the buyer's intention, or if the buyer is someone who uses these devices for both lawful and unlawful purposes, or if the seller is doubtful about his situation, then the view of the majority of scholars is that it is permissible. If someone uses them for unlawful purposes, the sin of that falls upon him alone.