Never encountered an actual 'Sergei', but two punts (happily in the distant past) come to mind:
Visited a massage parlour ( back in the day when they where brothels and not massage joints) in Edinburgh, near Murray field stadium.
There was a guy on the door, older chap, in a heavy overcoat and greasy hat. Welcoming enough and friendly, but with an impenetrable accent. Was very explicit in detailing what each girl was good at.
I went to an AW girls house to be met by her husband. Asked if I'd booked, quoted the price and took the.money. He stepped back into the living room carefully and somewhat eagerly counting the cash. Woman called to me from upstairs.
Afterwards he met me at the bottom of the stairs, asked if everything had been OK, and said to be sure and return.
There was something rather off about the whole meet, like maybe he had a drug problem and was pimping out the missus to feed it. She didn't volunteer any info and I didn't ask.