To be sure, there are two steps in their process: convince you their assessment is a valid reflection of the construct (term) of interest, and then examine diff

To be sure, there are two steps in their process: convince you their assessment is a valid reflection of the construct (term) of interest, and then examine different properties of the assessment (e.g. how reliable are a person's responses to this assessment). The convince you part is why it is not necessarily the reification fallacy. For example, suppose I create a measure of sadness that is the sole question: are you sad?. Does it seem like a good measure of the term sadness to you? If you think it's a bad measure,then I haven't convinced you, and we need to rethink a more convincing assessment, but it doesn't mean that if I use that question to operationalize (serve as my behavioral definition for) sadness that I committed the reification fallacy. Instead, you've failed to recognize that I'm using an argument of the form, "if you believe this is a good behavioral definition of sadness, then...". If you could ever see yourself using a statment like "that person is sad", then there are probably observables I could use to do research based on what sadness means to you. That's basically the logic these and many researchers in psychology / neuroscience are taking.