A genuine employment offer--verified and in writing--would be most important. There is also the possibility of a disagreement between whether the TN visa applicant is qualified according to the rules promulgated by USCIS for the issuance of a TN visa to the applicant, and the perception of qualification by the employer giving rise to its job offer. But CBP is just as likely to defer to the genuineness of the employment offer as proof of the sufficiency of the applicant's job qualifications.