We present a case study that utilizes community-based participatory research principles, community-organizing, and evaluation processes as an example of how to conduct community-based research to maximize compliance with policy implementation on tobacco sales in the retail environment. The study covers five different vulnerable communities in Los Angeles, California, including socioeconomically disadvantaged African American, American Indian, Hispanic Americans, Korean, and non-Hispanic Whites. We document barriers to compliance with the U.S. Food and Drug Administration, a government authority in charge of implementing tobacco policy. The case study presents a step-by-step community-based participatory research process with community-organizing principles to help guide the conduct of similar types of research. We discuss development and implementation of culturally tailored and language-specific research protocols. We provide examples of instrumentation development and make a case for community-based research on tobacco control in vulnerable populations. Our research design utilizes a mixed-methods approach, including qualitative (focus groups with key opinion leaders) and quantitative methods via retailer surveys and store audits/observations. We highlight lessons learned and benefits of community inclusion in conducting this type of research.