The definition and underpinning economic theory of market-based instruments (MBIs) for ecosystem services (ES) are yet unsettled matters. A refinement of their scope and a careful use of terms might facilitate communication among stakeholders and policy-makers. This article thus answers the research question: "How are MBIs for ecosystem services defined, reflected and assessed?". We analyse a sample of 106 peer-reviewed articles, which is representative of the scientific literature. The sample is distributed in the categories of a published typology to map existing instruments; yet their multidimensionality is challenging. We further find that a great diversity of research methods and evaluation criteria, as well as terms, is used in the literature. It is also observed that a large number of articles does not use scientific methods with new data, but resort to mere advocacy instead. This lack of a common theoretical and empirical framework, as well as consensus or comparative studies that would strengthen their conclusions, makes it difficult for practitioners to draw robust policy-relevant results. Interestingly, the articles presenting positive, negative, and mixed results were in almost similar proportions in our review. Therefore the application of harmonized assessment methods to better defined categories of MBIs with key shared characteristics might support evidence-based policies. For instance funding, incentive and allocation instruments should be more consistently differentiated.