Unless they are trying to push you around on the basis of their assumed identity, it's polite to treat people as what they claim to be. I once needlessly offended a transsexual by telling her I couldn't see her as a girl; it was true, but there wasn't any need to say it.

If someone presents as a Dom(me), and your Dom instinct tells you sie could fall at your feet and submit at the drop of a hint, don't say so: just drop those hints and let it happen. It's far more satisfactory when it leaves hir bewildered and astonished :-)