In my opinion the 03 was their best year. I have two of them, and both have been rode hard and put up wet. That said, my personal bike, when I got it had to be completely rewired, because the guy that owned it didn't have a clue about how the wiring and EHC worked. But the other 03 I have in my possession, has almost 23000 miles on it and hasn't had any problems at all.
Ask if it has the original EHC, or if it has been upgraded to something else.
Where has he had the maintenance done, and what has he had to do to it.
What oil has he been running in it.
I'm sure others will add to the list, but you really can't go to wrong with the 03.