No it doesn't matter what clients wear, at least not to me.
I usually ask clients to shower before the booking or upon arrival, but some people are extremely polite and concerned with doing the right thing, so I assume they have already showered.. particularly if they booked me for over an hour. Maybe it's naive of me.
When I used to receive from home or when I worked from spas, I absolutely didn't trust my clients to shower so I reminded them or had them shower right away. It's very very rare that a client came with bad hygiene, which is great news.
It also depends on the weather honestly. If it's hot or humid outside even if I trust my client that he showered at home, I'm going to insist..