Just about everything in the DSM is diagnosed by observation/questioning only. Psychiatric problems are usually not biologically diagnosable with the exception of brain injury (caused internally or externally like by a tumor, bleeding or a car crash or something) or genetic birth defects/development disorders like down syndrome.
Brainwashing is usually done by putting the brain in a traumatic/high stress situation while repeating whatever the goal is to wash it with. This can be achieved in many ways.
Ethics between a psychiatrist and patient are among other things confidentiality: A psych can only talk about anything you say to him if he has your permission to do so or when there is danger to the patient or others (in the latter case the people they can talk to are very restricted too) Strictly one-way relationships (psychiatrist doesn't reveal anything about themselves and can't get personally involved with a patient on any level).
That's all I know, but I'm not an expert, just a geek with too much wikipedia time on her hands