Some SPs will mention in their correspondence that a shower is available (most considerate clients if coming from a physically demanding/sweaty job will get out ahead of that and ask) and offer one with fresh towels and soap ready.
There's many too who will just insist every client shower on arrival, regardless of what time they last showered, to circumvent that whole issue. It can be challenging to assert oneself sometimes, but that gets easier with practice.
And some might choose to stop the session if it cannot be tuned out, and insist someone shower. Or may leave it for the appointment, but if the client reaches out to book again, say something then. It's an awkward conversation and one I personally have very rarely needed to have. Sometimes the client is genuinely unaware, like they may have a diminished sense of smell or similar, and they are then appreciative of the information.
Things like age, race and build are perfectly reasonable to ask. It doesn't mean discrimination- if you host out of a private apartment or hotel, it's rare to happen but the wrong person could knock on your door when you're expecting someone. It's a way to make sure the right person is at your door. I agree with you that if they're not willing to share such basic information, something's fishy.