The D-spin is pretty much set like any cork trick, so technically, its a really really off axis cork. Heres the main ways to tell:
Cork = Skiers feet never go above the persons head.
D-spin = Skiers feet go over his head, but the feet are never directly over his/her head at any time.
Rodeo = Skiers feet end up directly above his head during the trick.
Cork 7:
http://media.nscdn.com/uploads/member/videos/1143581347bigairjay%20002.mpg
D-spin 7:
http://media.nscdn.com/uploads/member/videos/9444SundayRiverdspin.mpg
Rodeo 7:
http://media.nscdn.com/uploads/member/videos/MikeWilson-Rodeo7Critical.wmv
Misty 7:
http://media.nscdn.com/uploads/member/videos/1143670174misty 720 nice.avi
There you go, best examples I could find. All skiers are spinning left to make things comparable.