Imagine you meet a provider at her place and she doesn't quite look like her pictures, or rather you found her pictures attractive but didn't really take a liking to her face-to-face.  You bite the bullet, and she proceeds with her role, and at this point you realize there's really no chemistry.  So say, you spent 15 minutes into an hour session.  Do you pay what is owed to her for the 15 minutes and maybe a little extra, or do you at this point owe her all the money?

not sure exactly what "didn't really take a liking to her face to face" or "proceeds with her role" means. However, based on my interpretation of those two comments, pay her in full.  

If you do not wish to pay for the entire hour, the don't give her a $100 cancelation fee & apologize.  I require a 50% deposit to book, so this would not happen to me.  If it did I would still expect some compensation for reserving my time.

Generally you pay it all..
Exceptions, Her pictures were not hers but you should leave immediately
She did or said something that was not true that lead you to book but again you should leave immediately.

So did you pay her or short her?

If she agrees about lack of chemistry, she may cut you a break.  But learn from this and make better choices going forward.

If she doesn't look like the pictures and you don't like that then turn around at the door and leave. Don't pay anything. But once you start things, you've committed and out of luck.

When the clothing drops, the bullshit stops. PTL doesn't mean praise the  Lord, it means pay the lady.

Cause if this isn't a joke then your a fool for asking this questions.  Try going to small claims court and asking judge  Judy!    

Yes, this is a hypothetical scenario!  

if you book an hour you have to pay an hour even if you stay less than that

You pay your money, you takes your chances...