What is the ruling on marketing hotel offers or airline tickets if the hotels serve alcohol or have mixed-gender rooms, knowing that the marketer's commission is calculated even if the customer books another hotel that offers prohibited things through the website?

If the marketer limits himself to marketing only hotels that do not offer forbidden things, then there is no harm in his work and his commission. The responsibility lies with the client if he chooses another hotel, for the marketer does not directly assist in a reprehensible act, nor is that his intention.