In a corporal stimulating massage, it is better to be naked with no towell on, anyway since you are in professional hands you can ask for a variation:
-You can be nude but you can tell me not to touch your genitalia (in case you fell uncorfortable having a man doing that)
-You can cover your intimate parts with a towell or wear underwear during the massage and I can pass my hands over the fabric.
– You can visit me with your love one, and I can guide him/her to do the movements. (Of course an amateur won´t perform the same, but if that make you feel better, that is a good option.
-You can even ask me for a theorical stimulation massage, I wont touch you, but you can learn some movements that you will later enjoy with your love one. Or you can visit me with your couple and learn together. Indeed this is a very good option.