For a challenge, get naked and sit in the chair with a boner. End is either verry happy or sad, no middle ground. ( If they have a sofa with a towel on opposite a mirror, your good to go)
Seriously, before that, you know in the opening moments, flirt and complement her as you pay in the room. Tell her how lucky you are to have a pretty girl massage, if she is touching your arm and calling you naughty, its time to feel her bum. Cold stare and nothings on.