The phrase "buying in to" is often used to describe acceptance or support for an idea or concept. However, there are several antonyms for this phrase that convey a lack of acceptance or agreement. One such antonym is "rejecting," which means to refuse to accept or believe something. Another antonym is "disagreeing," which means to hold a different opinion or view than someone else. Additionally, "doubting" can be an antonym for "buying in to," as it indicates a lack of conviction or confidence in a particular idea. Finally, "opposing" can be an antonym for "buying in to," as it suggests actively resisting or challenging a particular concept or idea.