In my state, patients are assumed to have capacity and it is incumbent on the physician to show why they do not.
I agree with
@whopper's approach in that a frank conversation about why I'm there and what the patient can potentially gain from the evaluation will typically coax some degree of cooperation. In those cases, I am usually very direct with the interview and do only the minimum needed for the consult. This approach is typically successful with the overwhelming number of "uncooperative" patients.
If that doesn't work, however, I will try to get the patient to talk about anything to get a sense of their mentation. If they refuse to cooperate but there's no evidence of acute cognitive impairment or decompensation, I will typically state that they have capacity but document my concerns in the note - i.e., that I believe that they have capacity based on their general mental status but that I was unable to talk about [whatever decision] specifically with them. If there are other clinical factors that might explain why they are uncooperative and/or would suggest that they don't have capacity - for example, somewhat acutely intoxicated with a high BAL, someone acute intoxicated in a substance (e.g., methamphetamine), medical derangements which might reasonably cause a delirium, etc. - and there is some evidence that they are not mentating clearly, I will typically opine that they don't have capacity and state that their inability/unwillingness to cooperate is secondary to those factors, which would suggest that they cannot reasonably participate in a discussion about risks/benefits for a medical procedure.
There's a lot of gray area in these questions sometimes. Applebaum's framework is nice, but it can very quickly go out the window with some patients.
