The potential for financial conflicts of interest (COIs) to damage the credibility of scientific research has become a significant social concern, especially in the wake of high-profile incidents involving the pharmaceutical, tobacco, fossil-fuel, and chemical industries. Scientists and policy makers have debated whether the presence of financial COIs should count as a reason for treating research with suspicion or whether research should instead be evaluated solely based on its scientific quality. This paper examines a recent proposal to develop criteria for evaluating the credibility of research without considering its source of funding. It concludes that proposals of this sort are likely to be either ineffective or impractical in many cases. Nevertheless, this does not imply that all research funded by those with an interest in the outcome must be placed under a cloud of suspicion; there are conditions under which research is at much more serious risk of being corrupted than in other cases, and attention to these conditions can guide productive responses to financial COIs.