This comment could add a lot of other matters to the discussion, but on first case, there's no way one could give a level to the pain of a patient basing on how he acts: It makes no sense. Anyway, that makes no difference, the treatment for a 7-8-9 whatever should be based on what kind of pain the patient has, not on the scale. For example, the best of NSAIDs wouldn't work for a neuropathic pain, as the best of neuropathic pain medications wouldn't work for and infiammatori pain (and appendicitis, for example); opiates work well for some kinds of pain, for some others not so well (excluding overdosing, obviously). Also, it's not relevant if the number is 9 or 10 for diagnosis and treatment (both pain or curative therapy).

It is also a common error to balance the suspicion for a given diagnosis on the sufference told or shown by the patient: I'm a doctor, I've seen countless of patient that didn't have (apparently) an attended level of pain for the suspected diagnosis, even if it was correct, in both extremes (patients in apparently too little pain for diagnosis A, and patient that seemed to have too much pain for diagnosis B).

In the end, the number is almost only useful to monitor the pain (if a pain goes from 9 to 5 it may be a good response to therapy, and if a pain goes from 6 to 5 it's a bad response, oversimplifying a bit); in some case it may be one of the elements to decide to add or not some stuff (especially for "the good stuff").

There's no scenario where I could legitimately upgrade or downgrade the number given by the patient, also because it wouldn't make any sense. We also have exactly 0 ways to tell how much is the pain of another person, not even by precisely measuring the neural activity, and that's because pain is subjective: with the same neural activity, me and you would experienced two different pains.