I believe Harav Moshe Feinstein ZT”L has a t’shuvah on this topic.
If I remember correctly he says that if it’s not for religious
reasons or a REAL problem w/ shidduch for the child,
(not any personal preferences) the child is not required to listen to the parents. It goes w/o saying that the child has to explain only respectfully that the shidduch is ultimately for
him and therefore his decision. This is no heter in any form to be disrespectful to ones parents.