I agree that a girl's comfort level with you is the most important factor, even when she really could use the extra cash.
It's also unpredictable: I mean, there's this masseuse, whose regular you have been for several years, but who basically has never been swayed - though there have been close calls!
And then there is this girl who you have only seen 2 or 3 times, for whom you have not done much, and who unexpectedly offers it all, with icings on the cake, for little to no surcharge: you weren't even thinking about it and you cannot understand why she has such a positive opinion of you.
This said, I do not understand why so many men are so driven to get full sex from masseuses: are there not plenty enough full service providers out there?
What more, massage is a distinctive pleasure and art-form; an opportunity to sit back, get lazy and be indulged.
Massage has yet another advantage over full sex; it allows skin on skin contact, a lovely lady's bare hands on your genitalia, instead of a rubber condom: is that not something?
So, if full sex is what you want, why not go straight to a full-service provider; but if you go to a masseuse, just learn to take what she gives and enjoy it as an end in itself?
I think first thing tomorrow I am going to call my veteran masseuse. Maybe this time I'll get lucky & she'll finally get around to climbing on that table and slide onto my shaft. She'd better be more skillful at slipping on condoms than I am...