They have a sense of entitlement to absolute power? Of course they do. They're paying you. If I pay you for goods or services then I am entitled to receive those goods or services. If I change my mind about a project then it's your job to counsel and advise me, but ultimately it's your job to do as I ask. If you can't do that then fire me as your client.
My clients pay me to perform services. They pay me to serve their needs. They do not pay me to serve my own needs. I do not take my ego into the business relationship. If they ask me for something to which I disagree then I talk to them about it. I explain why I disagree. I give them alternatives that I think better serve their needs. If they insist on doing things their way then that's their absolute right to do so. I either acquiesce or I fire them. There are no other alternatives.
Like it or not, agree with it or not, our job is to serve our clients, not ourselves. Our ego has no place in the equation. If their opposition to your recommendations are so egregious as to be untenable for you, walk away.
Let me recap:
If I am your client, then ultimately it's your job to serve me. That means doing what I ask. If you can't do that because you disagree with me then fire me as your client. Take your ego out of the relationship. It has no place there. Stop serving yourself and start serving your client.