It's the old Emperor's New Clothes scam. If you take the massage you lose weight, if you pay 50,000 you won't talk about how you were fooled. The only problem us the lack of condom use means some customers may experience weight gain over the next nine months.
I like funny sexual-escalation stories which involve a sweet-but-gullible girl who keeps getting drawn in deeper and deeper, until she's finally getting fucked silly without quite understanding how it happened. The best examples are the four "Nadeshiko-san Just Can't Say No!" chapters by Mojarin.
Ah yes...Just the legs...Because surely it will end with just that, right? Surely.
Still, sexercise is certainly always a great way to lose weight! Guaranteed results in no time (depending on how often you do it).
See Mojarin's "Nadeshiko-san Just Can't Say No! Massage" for a very similar story. You will probably enjoy all the other misadventures of the hapless, gullible Nadeshiko, too.
Also, see "Loosening Up Taniuchi-san," by the same artist.
Page 3, bottom panel ... in the words of the late great Adam West: "It Smells Like A Trap."
Subsequent events proved that to be true; could be the only reason this operator hasn't been shut down or arrested up till now is that each of the ladies who have undergone the *koff-koff* "treatment" have unconsciously agreed: "Hey Mikey, I Think She Likes It."
Oh Well ... sometimes it's like that in the H-Universe.