Taking blood is exactly that: it's literally sucking the life force out of you. I can't look because the sight of my blood being siphoned into that beaker makes me noxious. No such issue watching a tattoo needle do its work.
Finding a good artist based on a portfolio doesn't speak to sanitation. You're right though, there is a fine line between being careless and having trust. Just hard to understand where that line is. I appreciate your feedback.