Abstract There are calls to ground policies aimed at addressing the illegal wildlife trade (IWT), and biodiversity conservation more generally, on the best available evidence. However, evidence on IWT can be highly uncertain and difficult to obtain due to the illegal nature of the trade. Even when the evidence exists, there are numerous barriers to its uptake by decision makers, pertaining to the evidence itself and to the characteristics and contexts of those using it. The surfacing of the illegal trade in jaguars Panthera onca provides an example of how evidence is, and is not, used for decision‐making on IWT. We interviewed 38 conservation practitioners in Belize, Guatemala and Honduras, who had knowledge about, or experience dealing with, illegal jaguar trade. Interviewees described their information sources and decision‐making processes, and explicitly and implicitly prioritized jaguar trade evidence, based on attributes like the evidence's source, the scale and purpose of the trade, its temporal and spatial dimensions and the nationality of offenders. Even though interviewees stated that they use scientific evidence to make decisions, they gave more weight to evidence involving foreign actors and commercial purposes than local and non‐commercial ones, paying less attention to the potential impact on jaguars or the source of the information. They were also more inclined to favour events that were spatially and temporally closer to their own reality. Our results show that the interpretation and uptake of evidence are subject to contextual constraints and personal biases, which are common across fields and sectors, even amongst experienced decision makers. We propose an approach for evaluating evidence and informing decision‐making within IWT and biodiversity conservation. Our approach aims to guide conservation decision makers and practitioners to assess the relevance and uncertainty of the evidence, to recognize their own interpretation biases, to identify the actions that are appropriate based on the evidence and to improve the transparency of their decisions. It can also guide evidence ‘producers’ to develop evidence that is more aligned to conservation policy and practice. This approach can contribute towards more evidence‐based practice within the field of biodiversity conservation, with applications to IWT and beyond. A free Plain Language Summary can be found within the Supporting Information of this article.