I have never taken the initiative to ask a provider about a recommendation for another provider, but twice I have had providers recommend someone else. The only time I raised the question of another provider with the one I was with was to share amazement at what some of the girls would do (BBFS and BBA with no screening, full body and face photos with distinct tattoos that would be visible in casual street clothes. The conversation was more in the "I would never dream of doing that"/ "I am going to stay far away" mode than seeking a recommendation.
The first time was with a Thai Gal working in the DMV who recommended a friend and introduced me to the woman in the other bedroom of their apartment on the way out. I ended up seeing the friend more than the original provider. I don't think this was anything but friendship and the first provider wasn't getting a referral fee so far as I could tell.
The second time was with a Thai 48 hour escort and tour guide in Bangkok. Just after we met in my hotel room, she told me that her English wasn't as good as the agency made it out to be and that if I was interested in lots of sex, including a very extensive menu (DATY, DATO, anal, etc.), she would swap herself out for another girl at the agency who would be better for that. We had only been talking for 20-30 minutes, but I knew that the personality of the gal in front of me (very up front, forceful) was what I wanted on the tour guide side, so I stuck with her. I made the right decision. She wasn't a licensed tour guide, but she was very effective in getting me around and past people trying to sell me things, and getting me through crowds by locking wrists and glaring at anyone who tried to cut between us. We shared interests (history, sightseeing, dining, and culture) and she didn't want to shop or bringing me to a jewelry shop where she got a kickback). The sex was unadventurous - mostly BBBJ, cuddling, and showering/bathing together (3 showers a day makes sense in Bangkok given the climate if you are outside a lot). Her English was fine, even if she was self-conscious about it.