I guess he must have found that there were sometimes problems, maybe when a girl didn't want to perform a particular service for a particular customer. But that's only a guess.

Sometimes a girl might, and I say might as we would really never know, service say a regular client a little different than a first timer,
Possibly because of familiarity and the fact that she would be more comfortable, but not by much I would assume.
Generally though you can nearly always expect the same great service and have a great experience with anyone there..