Just to comment on the "relaxation" issue:
Though that is not my favorite style of work, I feel that relaxation work is extremely important. The nervous system has such an effect on our whole body and mental state, and it is very difficult for many people to let themselves relax and give the nervous system a break.
Relaxation massage is so beneficial in that respect, and sometimes it is exactly what a body needs to be able to let go of muscular tension and begin the healing process.
I agree that we all work differently, and that is a true positive. Different clients need different approaches and personalities.
Which leads me back to the original question: There are many different ways of assessing, be it visual, palpation, interpreting client comments, etc. Sometimes it can be formal, such as using a postural chart, and other times it could be informal during an intake interview, or watching how someone holds themselves on the table.