Early on in the process, there were questionaires.
Self-found on line, the Baron-Cohen ones: they gave interesting numbers.
Finding like-minded individuals on AS message boards, that was a revelation.
Formal diagnosis included once again questionaires like the Baron-Cohen ones, but also an extensive interview with my mother concerning my early childhood (which opened my eyes a little), a three hour session one-to-one with the specialist, and another hour-long visit to review and consider her report.
Any professional working just from a questionaire,
now that would set alarm bells ringing.