A previous single-county study found that retail stores usually asked young-looking tobacco customers to show proof-of-age identification, but a large proportion of illegal tobacco sales to minors occurred after the customers had shown identification proving they were too young to purchase tobacco. We sought to investigate these findings on a larger scale. We obtained state reports for federal fiscal years 2017 and 2018 from a federal agency that tracks tobacco sales to supervised minors conducting compliance checks in retail stores. We used descriptive and multivariable logistic regression methods to determine (1) how often stores in 17 states requested identifications, (2) what proportion of violations occurred after identification requests, and (3) if violation rates differed when minors were required versus forbidden to carry identification. Stores asked minors for identification in 79.6% (95% confidence interval: 79.3%-80.8%) of compliance checks (N = 17 276). Violations after identification requests constituted 22.8% (95% confidence interval: 20.0%-25.6%; interstate range, 1.7%-66.2%) of all violations and were nearly 3 times as likely when minors were required to carry identification in compliance checks. Violations were 42% more likely when minors asked for a vaping product versus cigarettes. Stores that sell tobacco to underage customers are more likely to be detected and penalized when youth inspectors carry identification during undercover tobacco sales compliance checks. The new age-21 tobacco sales requirement presents an opportunity to require identifications be carried and address other long-standing weaknesses in compliance-check protocols to help combat the current adolescent vaping epidemic.