It's a bit odd. If I get clients who can't cum then I say to them "Do you want to finish yourself off, I can play with myself if that will help or talk dirty? Just tell me what you think will help"
I would find it a bit strange if they went off and just did it on their own in another room. But I do consider my bathroom to be a "working room" as I do offer showers, so I wouldn't feel too much as if it had gone over my boundaries.
I always put away all my personal stuff in the bathroom before a client arrives. Toothbrush, flannel, scrubby thing, etc. Luckily I have a big cupboard in my bathroom. So I just leave out the "spare" toothbrushes, mouthwash, and mens shower gel and deodorant. So if they make a mess of any sort, at least it will be not on my stuff.
That's reminded me, a client shouted me from the bathroom the other day for a clean towel (in a hotel). I went in and got him another from the wardrobe but I'd already pointed out the ones opn the shelf. Then I realised my fake tan had dripped on the "clean" towel, it looked like a skidmark
Oh god, I doubt I'll see him again!