Hmm, my experience with the Steiner spas has been different.
Thanks to my pre work before my Celebrity honeymoon cruise on the "OLD" cruise critic site I knew to beware of the hard sell tactics. When I went to get my massage on the Century I found that they were not pushy at all. I was all set to pounce back at them too.
So, I chalked that up to being in a Celebrity Aqua Spa.
But just this past Nov. on the Sensation I went for the massage/facial special ($60) and the therapist took the argument out of my hands by telling me that she was going to tell me about products but that I was in no way being pressured and if I didn't want to hear about them to tell her and she'd not give me the pitch. I asked her to skip the sales pitch and we got on wonderfully for the next 70 minutes or so.
So, I guess I'm lucky in this regard, but I think if you tell them up front then they'll back off.
I'll let you know what I find on the Mercury in April.