If it’s listed as one of her likes, then you should expect her to do it.
Many will charge extra though, so I will normally establish this before the booking, that way it’s not such an awkward conversation when you are with her.
When handing over the envelope, I’ll also make a point of saying there’s an extra X for the facial.
As for the event itself, try not to cum unexpectedly. Get yourself comfortable (personally, I prefer to stand) and just focus on what you want to do. When it’s time to give her the warning, I’ll just add something like “…on your face, babe”.
I’m inclined to agree with Bud$ that when they are making you cum, some WG’s will deliberately alter their aim, that said, I can only think of a couple of occasions where a facial has turned into a chin/pearl necklace. What I find more common is that if you hit them with a good early shot, they’ll flinch or instinctively move their head away whilst you’re still going.
The way I look at it though is if you’ve hit them with a good shot, then it’s mission accomplished.
