Absolutely true. Kim utterly hates to be tickled, but she wants to work so often that I have to turn her away purely for lack of funds. If you want/need the money bad enough, that's all that matters.
In my experience, a minimum of 95%.
Although, Patience was literally grinning with glee while I was setting up and muttering "Boy oh boy I am so lucky!", and when I asked her what she was on about, she nodded towards Lina and said, "I get to be tickled by HER!". I thought that was hilarious. She just could't wait to get started.
And although it's technically true everybody has a price, eventually practicality comes into play. Priti retired late last year and won't come back under any circumstances. I told a local celebrity "name your price", but she didn't want to be in a fetish video at all. If a girl says "yeah, I'll do it for a bajillion dollars", okay, that was her price, but few to none of us could actually meet it so the point's moo. Like a cow's a opinion.