I'd agree, of course one should set terms. If you don't, you'd believe in some sort of mystical ability of the Dom to see at once just what the sub wants and is willing to do, and never to fail. I wouldn't accept a Dom/me who saw themselves as infallible like that, or who would totally deny the right to refuse doing a particular thing : pee play, rimming or having face slapped hard, for instance - or to have any limits (though I know some Doms would inisist that a sub is chattel,a piece of meat, and can really have no limits at all)

It's not like you know the Dominant full-on from teh beginning and I really would say any sub/slave merits the respect and dignity of a human being, a grown-up person.