The sage Shackleton says,
Once you've started the activities and the donation has changed hands, it's hers and not yours. ... The hobby doesn't come with a money back guarantee.
And he's exactly right. As a lawyer, I spend a lot of time that doesn't appear on your bill preparing for any initial meetings we may have -- doing a conflict check, making sure my assistants get materials prepared for our meeting, making sure I'm up to date on current law that may impact your matter.
The best and most professional of our lovely friends obviously also spend a lot of screening and prep time before we show up. If it's just a matter of bad chemistry or not clicking, it would be rude and wrong for us not to honor that preparation in full. If it's more than a matter of clicking or chemistry (like bait and switch, unsafe neighborhood, pimp-daddy hanging out in the next room, etc.), then you have the full chance to bail before the fee switches hands. (And you should use this forum to warn the rest of us.) But even if you have been duped and the money's already gone, you're much better shrugging off the loss and moving on.
I've only had one situation where the session didn't start well -- even though the lady was lovely as advertised, something just didn't seem right between us, and I couldn't really say it was either of our faults. We hadn't engaged in any services (other than strained conversation) up to that point, but I excused myself, saying something lame like "Hey, it's me not you." She gave an equally awkward comeback about how it just wasn't right somehow, and offered my fee back. I refused it, she insisted, we settled for me taking back half (some of which I spent sending her a gift with a note thanking her for her graciousness in a bad situation). I didn't review the encounter because I had nothing to say that would help the brotherhood (really, it was just a chemistry thing), and she didn't say anything bad about me to screw up my screening cred. I guess that was the best of a bad situation, but it wouldn't have been possible if I had demanded my money back.