Originally Posted By: callithump

Returning to the context, what's the best or safest way to address a group or a single person in face with respect, without the knowledge of their/his/her age or marriage status?

My choice is "Esteemed ________". In the case of a presentation, you might make this "Esteemed jurors" or "Esteemed examiners", depending on which you feel more appropriate. When addressing a larger group, "Esteemed listeners" or "Esteemed audience" works well. If they are your peers, "Esteemed colleagues" is a good choice. None of the listed choices refers to sex, age or marital status, which you might find helpful. I don't know if I would use it to address a single person, however. I would probably just use, as you suggested, "Good morning/afternoon". Remember that you will always need to take into account expressions of personal taste in the forums on this site. While some might find my choices stiff or overformal, I would deliver them with a warm smile, and I feel they would be well received. I hope this helps! :0)