Don't think that I've ever been refused by a BG except Estrella of Hong Kong who said she didn't go upstairs but I believe her because I've seen her with many guys and never has she ever gone arriba with any of them. The first time we met, I was with a friend of mine who fell for her hard. He was pretty drunk and was going to ask her up but he backed down because he was afraid he wouldn't be able to perform. The next time I found myself in HK, I sat down with her and bought her a drink and eventually asked her up but she politely refused and said she didn't go arriba.
I've been refused by a few SGs and I really have no idea why. (Usually, if you're the one that began the conversation/negotiation with the SG, you have to work hard to extricate yourself from her if you decide she's not for you.) I think maybe it was because I tried to speak my horrible Spanish with them and they instantly sensed that I was a very dorky gringo who was unworthy of their attention. (I read later on that one of the SGs who refused me was famous for turning down guys.) I'm not good-looking, by any means, but I'm not ugly or overweight, either, so I don't think that was the reason.
It is rare, to say the least, that one of the chicas turns down a paying client.