My personal view on this is that CAD D is harmless.
CAD D goes under as light damage, panel damage, broken arms, dents ect Not at all Chassis damage or any major parts, like engine.
The only thing that would depreciate this car more than normal 350z would be the repair job done on it. You can see from the picture that the colour match is not too bad so that a good sign I guess.
To find out more about the damage, did any airbags go off. If no airbags went off, I would say that at 5k it is a bargain, but being on ebay it is bound to go up to 6k +.
Looks like a good buy if you ask me!