I’ll re-emphasize my point: it’s the way of communicating that seems at issue. A sitter asking a question or making a request in a tactful & friendly manner shouldn’t cause a Host to jump straight to “you’re a guest in my home & here it’s my way or the highway; I think we should cancel the sit.”
But we can agree to disagree without any further elaboration at this point; I don’t think we’re in any danger of coming across one another on a sit. 
I don’t know if you realise but, your language illustrates precisely the hierarchical mindset that @MerryPuppins is alluding to.
Your response is arguably more revealing than you realise. 
For what it’s worth, once a sitter has spent time in our home and with our pets and has a much better understanding of how things actually are, I’m much more receptive to their feedback, in fact I ask for ways to improve the sit when it’s over. I respect that some sitters have more experience with animals than I do and I welcome their advice.
Someone passing judgement on the right way to do things without ever having set foot in my house or interacted with my pets is another matter entirely.
Mostly I’d agree that hosts get to ‘ask’ sitters to follow their preferred pet care regime however there are red lines…..and we’ve read about some of these in multiple threads. I recall a few notable ones, one being having the sitter chew up fillet steak in their own mouth before feeding tiny pieces it to a dog… (did I dream that one?!) I think as a general principle it’s perfectly ok for sitters to question aspects of a particular regime, and to have a discussion prior to a sit.