Sixer,
You're right as far as it goes, however, I was once in a spa in Pickering where the MPA finished the session, and left the room to go to the attendant's area. The guy turned on the shower, through on his clothes and ran out the door to his truck, and peeled rubber as the attendant came out to the lobby. He stiffed her for a 1 hr session plus whatever extra's she provided. Based on how pissed she was (I didn't blame her at all) she must have either provided FS or NR.
After that experience, when I agree to extra's (usually right at the start of the session) I pay upfront. Many girls have said "It's OK, we can settle later." but I would rather have her mind on the task, not thinking about how much $$ is she going to get. Since I tend to tip $20 more than average, I never have problems with the quality of the service.
Once I get to know the attendant, than it's not really a problem.
When I was in Edmonton in the 80's it was common for the attendant to ask the extra's fee before providing the extra. Haven't found that to be the case in TO.