I recently saw a local provider.  It was good but not great, so I would like to try someone else. How do I ask the first lady for a reference?

stating that you have an appointment, the lady requires a reference, and would it be okay to give her contact information to the lady you're going to see.

Or you can give the second provider the first providers info.and they will chat. it is standard procedure. They will not chat about specifics of the date, dont worry. Just that you are a legit hobbyist

The question I was asking was a common courtesy one- I am assuming that one should let provider #1 know she will be called. How does one politely say "you are being dumped for another girl"?

The major attraction to the hobby for most is not commitment. Just ask her if she is ref friendly.

Most prostitutes know that the patrons bounce from woman to woman.  There is usually no offense taken if you see another woman.  

I wouldn't worry about that.