Some graphologists are hoaxsters, but there are legitimate observations made by a few who've spent many years at it.
Signs of deception, such as "overstrokes" in the letter formations, and recognition of certain style traits, such as serifs, may be useful in forming a profile of the writer.
Most people who are intentionally disguising their handwriting cannot completely hide clues to their identity.
You may be right (although I would change "some" to "most," even so), but during the 20+ years I spent in, shall we say, a related field, I never met a single one who was able to back up his/her claims. It's telling, I think, that certified handwriting analysts (those who only try to connect specific writers with particular writings) are accepted in every court in the land as "expert witnesses," while so far as I know, such status has never been extended to even one graphologist.
I suppose it's possible I just met all the wrong graphologists...