The correct spelling of the word "wert insincere with" is actually "were insincere with." The "wert" suggests an archaic use of the second person singular past tense of "be," which is now mostly replaced by "were." The word "insincere" is pronounced /ɪnˈsɪnsɪə/, with the stress on the second syllable. Finally, the preposition "with" is pronounced /wɪð/, rhyming with "fifth." It's important to pay attention to spelling and pronunciation nuances to avoid confusion and sound more professional.