Him: Hi Becky. I saw your ad on Eros. I wanted to ask if you could do outcall for me, but it's be sort of a trial.

Sexy Becky:  Can you please explain to me what you mean by a sort of trial?

Him: I would not pay you besides maybe a small deposit, however if you do a good enough job satisfying me, I will book you every week and pay you in full. Would you be open to that?

Sexy Becky: Are you losing your mind? I don't think so.  

Him:  No, I'm not. I want to find a permanent girl, and this is the most effective way to determine who is good enough for that.

END OF MESSAGE

END OF MESSAGE

Because it was a dumb idea. Why in the world would a girl book a session with you and potentially get only a fraction of her rate? Only the most desperate would agree.
Not only that, all she did was turn you down. She didn't flame you or threaten to BL you. So you're whining about nothing.

this sounds like a Nigerian prince or Indian IRS scam.