This gives me flashbacks of the time when the receptionist (And I think it's the same girl receptionist OP is referring to) made me wait 1 and a half hour and, although I had booked the girl and came 10 minutes early, she let the customer before me extend for an hour.
The only difference is I hate confrontation so I quietly left after the session.
The session was good though as it was with Ginza's Mocha who did a stint at M5 for few months.
From that day on, I only go to M5 to see regulars who have moved from other shops.

I also had long line of duds at the shop since 2010 till 2019 (Pretty sure mgmt changed hands couple times since 2010).
Having said that I also met 2 gem of a girl at M5: Thai Patty and Chinese Helen.
I still see Patty sometimes.