I start with casual visits to sample what the location has to offer. I eventually befriend the girls and the manager. It does require honesty for a friendship to be sustained, but I believe it is incumbent on us to create the environment where the girls want to tell us their truths.
My only exception to being truthful is when asking for "only you" services and they ask about that service and another girl at the spa. For example if Cindy asks "Did Dan Dan do this for you?", my consistent answer is "I don't know" which keeps a healthy boundary between them. If Cindy declines that service, I do ask for Dan Dan next time. It keeps it fresh for a few months, but I have favorite spas that I continue to visit years later.
When I have a great time, I get the girl's number. I have even visited a few after they move to other cities. It can be a little strange when they introduce me to their families, including there husband. I have even had a beer with these guys. I guess that is the price for an authentic friendship based on truth.