Now that I've found a masseur I really like I just book him over and over. But it took a while!
Short story:
Search Locanto and find someone with a video or certification so you know they're for real.
Long story:
In my experience, most spa masseurs are GAY and subtle or not-so-subtle suggestions just aren't going anywhere. I love Banyan Tree but the masseurs are all gay :p
The out-call massage agencies I found on the web didn't specialize in yoni. Seemed like an afterthought? So I passed on those.
You should search for people who specialized in yoni massage and don't settle until you find someone who makes you comfortable. I found a few yoni masseurs on Locanto (I didn't try Craiglist, bad reputation) and after chatting to one for a while and watching his video I felt it would be the real thing. Amazing hands lol
Do your homework!:)