I do not have first hand experience with this but I would like to help him make sure that his prospective sex workers are true professionals who care deeply about the health, safety, satisfaction and discretion of their clients, and who are operating independently will full professional control over their business--not even a suggestion of human trafficking or sexual slavery.
I have heard people like Dan Savage speak of websites designed to network independent sex workers and prospective clients during various podcasts, that put an emphasis on safety and discretion, but I'm having trouble finding any references to specific websites or organizations he or his guests recommend as he has literally hundreds of episodes an hour long each. I found two useful resources via google but *I know* there are more and better resources out there.
If any of you can offer some specific web resources that might help him locate a sex worker (emphasis on ethical, safe, discrete, professional service) that I may relay to him, I would be greatly appreciative.
Additionally if you have any specific recommendations such as questions to ask a prospective sex worker to help determine if they are the right fit for you (and you are the right fit for them), please feel free to include them as well.