Sorry to be lascivious here, but do we know it was head and not a handjob? I was always told that you went in, you laid down on your stomach with a towel around your waist, like a "regular" massage, and if it was one of "those" places, if you rolled over with money tucked into the front of the towel, the massage would no longer respect the boundaries of the towel (if you get my drift).
(For the record, I've never done this not for moral reasons, but because I can't figure out the mechanics of it. I'd be afraid of not having the right amount of $$ and/or getting the "what is THAT for?" rejection. Seriously. Though I'd be bothered by the morals of a woman doing it out of force or coercion.)