The phrase "were insincere with" can be replaced by several synonyms, depending on the context of the situation. Some examples include "deceived," "misled," "pretended," "faked," "hypocritical," and "dishonest." These words all imply a lack of honesty or genuineness in one's actions or words. "Deceived" suggests intentional actions to manipulate or trick someone, while "misled" implies a misunderstanding or confusion. "Pretended" and "faked" both suggest a deliberate act of pretending or acting. "Hypocritical" and "dishonest" suggest a lack of moral principle or ethical behavior. Ultimately, the choice of synonym depends on the specific circumstances and intended meaning.