A key challenge in conducting paid internet-based studies is that individuals may feign eligibility to participate. This case series describes three examples where people attempted to fake being locals with health vulnerabilities to participate in paid internet-mediated studies. In two cases, individuals pretended to have serious cancer diagnoses to participate in a randomized controlled trial. In the third case, an individual pretended to be nine restaurant workers at high risk of occupational COVID-19 exposure to participate in an online survey. Key (...) red flags among individuals feigning eligibility are noted. Ethical and practical methodologic implications are discussed. (shrink)