There's two different scenarios here: 1.) Tipping in a spa where the house takes a cut and 2.) Tipping an independent contractor who comes to your place/you go to theirs. (Basic math of a spa - $60 massage (let's say 30% goes to masseur = $20 + 20% tip = $32). So for someone in a spa you should tip remembering that the fee the masseur receives for the services is small and the bulk comes from your tip.
And scenario 2.) The whole fee goes to the masseur. $150 massage = $150. I think general consensus from this board is that, unless the independent contractor incurred some unexpected cost, that the fee is the fee ($Total = $150) and in a spa you should always tip to the level of service received.
