Is it permissible to rent a shop to an individual for the purpose of him making it a barbershop, knowing that he performs the "Qaza‘" haircut, which may be forbidden? And in this case, would the rental money be unlawful, and would the landlord be a partner in the sin?

Al-Qaza' is the shaving of part of the hair and leaving part of it, and it is disliked according to the majority of scholars, unless there is a need for it. Al-Nawawi said: "They (scholars) have unanimously agreed on its disliked nature if it is in scattered places, except for medicinal purposes." So, if al-Qaza' is disliked, then renting out a shop to someone who performs it is not considered unlawful nor does it affect the validity of the rental contract, and the rent of the shop is permissible.