Non-writing attorneys often don't know what to look for to assess the persuasiveness of writing. Is it not self-evident? Persuasive writing persuades more. But more than what? An attorney wanting to assess the merits of potential ghostwriters could accurately judge the comparative persuasiveness of briefs arguing the same position. Although I have never heard of an attorney comparing writers in this way, the method is powerful, where your choices are limited to a few ghostwriters. If you try to assess persuasiveness without a control, the halo effect will bias your estimate by your position’s tenability. The easier the position to defend, the more persuasive the writing will appear.
Absent a controlled experiment, an attorney hiring a ghostwriter must isolate some persuasive characteristics of writing, rather than introspect his personal persuasion. Of all writing's directly perceptible attributes, the most informative about the effectiveness of the writing as such is its sense of flow. Flow means that the reader is informed of the relationship between the sentences without unneeded cues interrupting his thoughts. Flow is the major part of Clarity and an important instrumentality of Concision and Euphony. Flow concerns managing transition, but it is undermined by a surfeit of interrupting transitional terms.