I also consider how she responds to me, and whether I think it's real or not.I choose a regular based on her appearance, service, price and how comfortable I feel around her.
Her incall location counts to.
I think that if they say they enjoyed your session and would like to see you again that's as close an indication of their interest as you will get.I've usually not repeated until very recently. I wonder if I'm starting to prefer the known experience rather than chasing the unknown and new.
As an SP, do you drop hints if you wanted someone to become a regular?