No I would not give them negative karma.
This is not yelp where a 4 out of 5 is consider very good, anything below a 5 is viewed as bad or at least makes someone seen as "questionable cuddler". So one bad karma could tank someone's ability to cuddle.
I don't want to be mixed up in causing that.
I would officially report we did not meet, just in case they try to do/say something to hurt me, but after that I would politely message them and let them know what they did was not acceptable, if they had an emergency it was their responsibility to inform me they couldn't make it (it takes less than ten seconds). I would tell them that I will not be leaving them any negative karma because if this was just a careless error I wouldn't want it to ruin their ability to find new clients. BUT I would tell them that I have a minority opinion and point out most would give them negative karma (I might even site this post and the poll), so this is not a kindness they should expect from others in the future should they continue with this behavior.
If this was a one off careless error, they will learn the lesson and be fine going forward, if this is a pattern they will quickly find others who will give them low karma tanking their cuddling careers. No need for me to sully my hands.
I'd leave a negative review if I were you. I owe one cuddle at a discounted rate to someone I had poor communication with twice! I doubt he's planning on replying to my last message. It stinks to have dropped the ball with him. Life happened and I fell short. If he had given me a negative Karma even though it would affect my reviews. It would've been understood. Negative customer experience, negative review. If the pro wanted to appeal it, along with charge of the sale, that's up to her.
I wouldn't stress it just leave that karma and move on.. sadly it happens if anything they lost your business. While I would love to hope that theres some type of emotional bond in the end you are paying for a service with a pro. They view it that way, you do too!