Sploshing is wet and messy. It could be food (whipped cream, pudding, chocolate sauce), mud, shaving cream, what have you. I suppose someone might call bukkakke sploshing, but I wouldn't.
What does it matter? I'm curious, that's all. It plainly is not as straightforward as all that. I know what I think is prostitution, and I know what my wife thinks is prostitution. But regardless of what the letter of the law says, I don't have a good idea of what LE thinks is worth pursuing as a prostitution related offense. For example, you can go to a rope bondage workshop or a club that has public paddilng, and that's all legal, right? But even if the paid model is enjoying it a little bit too much, I doubt the cops are gonna come and bust it up. Similarly, 10mph over the speed limit is speeding according to the letter of the law, but when do you ever get pulled over for that? For all intents and purposes, it isn't a problem.
Maybe this would make it more concrete. There's a CL ad from time to time from some girl who advertises as a sub for some corporal play (caning, paddling, etc). Is there any possibility that LE might try to sting some johns with an ad like that? That seems to me to be way less risky than most CL tuina ads, even in the therapeutic section, even though there is more obvious nudity and sexual energy involved, but I have no idea if it really is.