Asking anything should be part of the work. Trust is about us, not the other. If we allow ourselves to be vulnerable and the other was faking, then that's down to them. If we close ourselves down because of what someone else maybe, we are giving them power over our life's.
Be yourself with everyone, some will connect with you others because of their own wounds won't.
If a T is fake, whether to be vulnerable isn't the only issue.