That's a good question.
I've seen a foreign visiting prossie who was fantastic on the first visit. I booked her a second time on a Sunday afternoon and she was completly different in terms of service. She just wasn't bothered after I came. Anyway being a fluffy bastard I booked a third time on her second visit to the UK and she was back to her usual stellar self.
With a regular, who doesn't tour, I've always had good service every time. But I have noticed a slight annoyance on her part when I turned up too early once. And when I had a booking on a quiet day in the evening she wasn't in the right mood for the booking. I was in and out within the hour, usually I get some extra time as a semi regular client.
The prossies attitude can make or break the punt IMO.