You're right if it's an RMT giving the massage at a reputable place (which is what the thread is about, oops!), then it would take a number of visits and of course neither would say anything.
My mind went to semi-legits
and I was thinking about the case where you get a receipt from an "RMT" (to submit to insurance, I know, stupid move) and the name doesn't match the girl who gave you the massage (or maybe it does, still bad in the CMTO's eyes if extras are on the table). Not sure how the CMTO figures this out, but I've heard of cases of it happening and then they send in a guy as a plant. And in semi-legits, he'd probably get offered something even on the first visit
. Not sure why an RMT running (or working at) a semi-legit would risk giving out receipts, but it happens