“Broken Engagements” in Halachah, Hashkafah and Psychology

Why are there so many broken engagements nowadays? How can they be avoided? Does the one who breaks the shidduch get penalized? Do the ring, sheitel and other gifts need to be returned? Who pays the costs which were committed to (wedding hall, photographer, band, make-up artist)? Does the Shadchan need to return the Shadchanus?