YouTube videos of body massages are generally real. While the people on screen may be actors, the massage is still taking place, and it is being filmed as it happens.
On YouTube, it's common for massage therapists to upload videos of themselves working on clients, especially if the channel is a teaching channel. Through YouTube, massage therapist instructors are able to promote their businesses and show students how to perform a proper massage, especially if the students are learning from home. All the therapist has to do is to record a session with a client and upload the video to the service.