Consumers rely on the information on food packages to make informed choices. However, manufacturers may sometimes adopt inefficient labeling to establish a superior product image and charge price premiums. This study first focuses on labeling redundancy implied by the USDA Organic Seal and Non-GMO Project Verified (NGPV) mark on plant-based milk products, and statistically evaluates the price premiums attributable to their existence. In addition, this study characterizes and examines a second form of labeling inefficiency: trace amounts of unqualified ingredients permitted by certifying entities but not explicitly communicated to consumers. The researcher utilizes an innovative, incentive-compatible online survey with randomized information treatments to collect respondents’ willingness to pay for certified plant-based milk products, and quantifies the impact of enhanced consumer knowledge about the underlying facts. In short, exact dollar amounts associated with multiple forms of labeling inefficiency and information treatments are calculated; distinctive preferences are identified among consumers with dairy sensitivities and vegan or vegetarian status, as the former group preferred soy milk while the latter one favored oat milk; demand for oat milk decreased as consumer’s age increased; single presence of the USDA Organic Seal was more attractive than NGPV mark; there was a diminishing return instead of any synergy for dual-labeling; the product type of oat, age, household income and single presence of either the USDA Organic Seal or NGPV mark were significant stimuli attracting people to adopt soy and oat milk products; the public was relatively more informed about USDA Organic criteria; there was a strong bias among people who self-identified as being familiar with NGPV criteria; and finally, information about certification exceptions actually increased consumer WTP under the specific conditions of this study. Results of this study could facilitate consumer education, firm decisions and policymaking.