Is it permissible to sell an Internet cafe or return it to the seller, knowing the difficulty of using it for good, and that it may be used for matters that displease Allah, such as music, while only being able to block pornographic websites?

It is not permissible to sell a coffee shop to someone who will use it for unlawful purposes. As for returning it to its original owner, there is a difference of opinion among scholars: those who consider rescission (iqalah) a cancellation of the contract permit it, while those who consider it a new sale prohibit it if the seller knows it will be used for unlawful purposes.

The most prudent course of action for clearing one's conscience is to transform the coffee shop into a permissible venture, such as an educational center or a telecommunications center. "And whoever fears Allah - He will make for him a way out, and will provide for him from where he does not expect."